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-rw-r--r--lib/receiver/sch.c339
1 files changed, 0 insertions, 339 deletions
diff --git a/lib/receiver/sch.c b/lib/receiver/sch.c
deleted file mode 100644
index 3273237..0000000
--- a/lib/receiver/sch.c
+++ /dev/null
@@ -1,339 +0,0 @@
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
-#include <string.h>
-#include "gsm_constants.h"
-
-#define DEBUGF(a...) { \
- fprintf(stderr, "%s:%d ", __FILE__, __LINE__); \
- fprintf(stderr, a); \
-} while (0)
-
-
-
-/*
- * Synchronization channel.
- *
- * Timeslot Repeat length Frame Number (mod repeat length)
- * 0 51 1, 11, 21, 31, 41
- */
-
-/*
- * Parity (FIRE) for the GSM SCH.
- *
- * g(x) = x^10 + x^8 + x^6 + x^5 + x^4 + x^2 + 1
- */
-#define DATA_BLOCK_SIZE 25
-#define PARITY_SIZE 10
-#define TAIL_BITS_SIZE 4
-#define PARITY_OUTPUT_SIZE (DATA_BLOCK_SIZE + PARITY_SIZE + TAIL_BITS_SIZE)
-
-static const unsigned char parity_polynomial[PARITY_SIZE + 1] = {
- 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1
-};
-
-static const unsigned char parity_remainder[PARITY_SIZE] = {
- 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
-};
-
-
-static void parity_encode(unsigned char *d, unsigned char *p)
-{
-
- unsigned int i;
- unsigned char buf[DATA_BLOCK_SIZE + PARITY_SIZE], *q;
-
- memcpy(buf, d, DATA_BLOCK_SIZE);
- memset(buf + DATA_BLOCK_SIZE, 0, PARITY_SIZE);
-
- for (q = buf; q < buf + DATA_BLOCK_SIZE; q++)
- if (*q)
- for (i = 0; i < PARITY_SIZE + 1; i++)
- q[i] ^= parity_polynomial[i];
- for (i = 0; i < PARITY_SIZE; i++)
- p[i] = !buf[DATA_BLOCK_SIZE + i];
-}
-
-
-static int parity_check(unsigned char *d)
-{
-
- unsigned int i;
- unsigned char buf[DATA_BLOCK_SIZE + PARITY_SIZE], *q;
-
- memcpy(buf, d, DATA_BLOCK_SIZE + PARITY_SIZE);
-
- for (q = buf; q < buf + DATA_BLOCK_SIZE; q++)
- if (*q)
- for (i = 0; i < PARITY_SIZE + 1; i++)
- q[i] ^= parity_polynomial[i];
- return memcmp(buf + DATA_BLOCK_SIZE, parity_remainder, PARITY_SIZE);
-}
-
-
-/*
- * Convolutional encoding and Viterbi decoding for the GSM SCH.
- * (Equivalent to the GSM SACCH.)
- *
- * G_0 = 1 + x^3 + x^4
- * G_1 = 1 + x + x^3 + x^4
- *
- * i.e.,
- *
- * c_{2k} = u_k + u_{k - 3} + u_{k - 4}
- * c_{2k + 1} = u_k + u_{k - 1} + u_{k - 3} + u_{k - 4}
- */
-#define CONV_INPUT_SIZE PARITY_OUTPUT_SIZE
-#define CONV_SIZE (2 * CONV_INPUT_SIZE)
-#define K 5
-#define MAX_ERROR (2 * CONV_INPUT_SIZE + 1)
-
-
-/*
- * Given the current state and input bit, what are the output bits?
- *
- * encode[current_state][input_bit]
- */
-static const unsigned int encode[1 << (K - 1)][2] = {
- {0, 3}, {3, 0}, {3, 0}, {0, 3},
- {0, 3}, {3, 0}, {3, 0}, {0, 3},
- {1, 2}, {2, 1}, {2, 1}, {1, 2},
- {1, 2}, {2, 1}, {2, 1}, {1, 2}
-};
-
-
-/*
- * Given the current state and input bit, what is the next state?
- *
- * next_state[current_state][input_bit]
- */
-static const unsigned int next_state[1 << (K - 1)][2] = {
- {0, 8}, {0, 8}, {1, 9}, {1, 9},
- {2, 10}, {2, 10}, {3, 11}, {3, 11},
- {4, 12}, {4, 12}, {5, 13}, {5, 13},
- {6, 14}, {6, 14}, {7, 15}, {7, 15}
-};
-
-
-/*
- * Given the previous state and the current state, what input bit caused
- * the transition? If it is impossible to transition between the two
- * states, the value is 2.
- *
- * prev_next_state[previous_state][current_state]
- */
-static const unsigned int prev_next_state[1 << (K - 1)][1 << (K - 1)] = {
- { 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2},
- { 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2},
- { 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2},
- { 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2},
- { 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2},
- { 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2},
- { 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2},
- { 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2},
- { 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2},
- { 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2},
- { 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2},
- { 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2},
- { 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2},
- { 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2},
- { 2, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1},
- { 2, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1}
-};
-
-
-static inline unsigned int hamming_distance2(unsigned int w)
-{
-
- return (w & 1) + !!(w & 2);
-}
-
-
-static void conv_encode(unsigned char *data, unsigned char *output)
-{
-
- unsigned int i, state = 0, o;
-
- // encode data
- for (i = 0; i < CONV_INPUT_SIZE; i++) {
- o = encode[state][data[i]];
- state = next_state[state][data[i]];
- *output++ = !!(o & 2);
- *output++ = o & 1;
- }
-}
-
-
-static int conv_decode(unsigned char *data, unsigned char *output)
-{
-
- int i, t;
- unsigned int rdata, state, nstate, b, o, distance, accumulated_error,
- min_state, min_error, cur_state;
-
- unsigned int ae[1 << (K - 1)];
- unsigned int nae[1 << (K - 1)]; // next accumulated error
- unsigned int state_history[1 << (K - 1)][CONV_INPUT_SIZE + 1];
-
- // initialize accumulated error, assume starting state is 0
- for (i = 0; i < (1 << (K - 1)); i++)
- ae[i] = nae[i] = MAX_ERROR;
- ae[0] = 0;
-
- // build trellis
- for (t = 0; t < CONV_INPUT_SIZE; t++) {
-
- // get received data symbol
- rdata = (data[2 * t] << 1) | data[2 * t + 1];
-
- // for each state
- for (state = 0; state < (1 << (K - 1)); state++) {
-
- // make sure this state is possible
- if (ae[state] >= MAX_ERROR)
- continue;
-
- // find all states we lead to
- for (b = 0; b < 2; b++) {
-
- // get next state given input bit b
- nstate = next_state[state][b];
-
- // find output for this transition
- o = encode[state][b];
-
- // calculate distance from received data
- distance = hamming_distance2(rdata ^ o);
-
- // choose surviving path
- accumulated_error = ae[state] + distance;
- if (accumulated_error < nae[nstate]) {
-
- // save error for surviving state
- nae[nstate] = accumulated_error;
-
- // update state history
- state_history[nstate][t + 1] = state;
- }
- }
- }
-
- // get accumulated error ready for next time slice
- for (i = 0; i < (1 << (K - 1)); i++) {
- ae[i] = nae[i];
- nae[i] = MAX_ERROR;
- }
- }
-
- // the final state is the state with the fewest errors
- min_state = (unsigned int) - 1;
- min_error = MAX_ERROR;
- for (i = 0; i < (1 << (K - 1)); i++) {
- if (ae[i] < min_error) {
- min_state = i;
- min_error = ae[i];
- }
- }
-
- // trace the path
- cur_state = min_state;
- for (t = CONV_INPUT_SIZE; t >= 1; t--) {
- min_state = cur_state;
- cur_state = state_history[cur_state][t]; // get previous
- output[t - 1] = prev_next_state[cur_state][min_state];
- }
-
- // return the number of errors detected (hard-decision)
- return min_error;
-}
-
-
-int decode_sch(const unsigned char *buf, int * t1_o, int * t2_o, int * t3_o, int * ncc_o, int * bcc_o)
-{
-
- int errors, t1, t2, t3p, t3, ncc, bcc;
- unsigned char data[CONV_SIZE], decoded_data[PARITY_OUTPUT_SIZE];
-
- // extract encoded data from synchronization burst
- /* buf, 39 bit */
- /* buf + 39 + 64 = 103, 39 */
- memcpy(data, buf, SCH_DATA_LEN);
- memcpy(data + SCH_DATA_LEN, buf + SCH_DATA_LEN + N_SYNC_BITS, SCH_DATA_LEN);
-
- // Viterbi decode
- if ((errors = conv_decode(data, decoded_data))) {
- // fprintf(stderr, "error: sch: conv_decode (%d)\n", errors);
- //DEBUGF("ERR: conv_decode %d\n", errors);
- //return errors;
- }
-
- // check parity
- if (parity_check(decoded_data)) {
- // fprintf(stderr, "error: sch: parity failed\n");
- //DEBUGF("ERR: parity_check failed\n");
- return 1;
- }
-
- // Synchronization channel information, 44.018 page 171. (V7.2.0)
- ncc =
- (decoded_data[ 7] << 2) |
- (decoded_data[ 6] << 1) |
- (decoded_data[ 5] << 0);
- bcc =
- (decoded_data[ 4] << 2) |
- (decoded_data[ 3] << 1) |
- (decoded_data[ 2] << 0);
- t1 =
- (decoded_data[ 1] << 10) |
- (decoded_data[ 0] << 9) |
- (decoded_data[15] << 8) |
- (decoded_data[14] << 7) |
- (decoded_data[13] << 6) |
- (decoded_data[12] << 5) |
- (decoded_data[11] << 4) |
- (decoded_data[10] << 3) |
- (decoded_data[ 9] << 2) |
- (decoded_data[ 8] << 1) |
- (decoded_data[23] << 0);
- t2 =
- (decoded_data[22] << 4) |
- (decoded_data[21] << 3) |
- (decoded_data[20] << 2) |
- (decoded_data[19] << 1) |
- (decoded_data[18] << 0);
- t3p =
- (decoded_data[17] << 2) |
- (decoded_data[16] << 1) |
- (decoded_data[24] << 0);
-
- t3 = 10 * t3p + 1;
-
- // modulo arithmetic t3 - t2 mod 26
-// tt = ((t3 + 26) - t2) % 26;
-
-// fn = (51 * 26 * t1) + (51 * tt) + t3;
-
- /*
- * BSIC: Base Station Identification Code
- * BCC: Base station Color Code
- * NCC: Network Color Code
- *
- * FN: Frame Number
- */
-
-// printf("bsic: %x (bcc: %u; ncc: %u)\tFN: %u\n", bsic, bsic & 7,
-// (bsic >> 3) & 7, fn);
-
-// if (fn_o)
-// *fn_o = fn;
-// if (bsic_o)
- if (t1_o && t2_o && t3_o && ncc_o && bcc_o) {
- *t1_o = t1;
- *t2_o = t2;
- *t3_o = t3;
- *bcc_o = bcc;
- *ncc_o = ncc;
- }
-
- return 0;
-}