[handover] Real handover algorithm
This implements the handover algorithm (and associated parameters)
as described in Chapter 8 of the book "Performance Enhancements in
a Frequency |Hopping GSM Network" by Thomas Toftegard Nielsen and Jeroen
Wigard.
The parameters such as averaging windows are configured in struct
gsm_network. We keep some state to trakc up to 10 neighbors as
they are being reported from the MS.
This has so far only been tested in a network with two BTS that
have each other as neighbor. Networks with morge neighbors might
encounter bugs.
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index d19f38b..8769558 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -143,6 +143,20 @@
unsigned int waiting_for_imei : 1;
};
+/* Maximum number of neighbor cells whose average we track */
+#define MAX_NEIGH_MEAS 10
+/* Maximum size of the averaging window for neighbor cells */
+#define MAX_WIN_NEIGH_AVG 10
+
+/* processed neighbor measurements for one cell */
+struct neigh_meas_proc {
+ u_int16_t arfcn;
+ u_int8_t bsic;
+ u_int8_t rxlev[MAX_WIN_NEIGH_AVG];
+ unsigned int rxlev_cnt;
+ u_int8_t last_seen_nr;
+};
+
#define MAX_A5_KEY_LEN (128/8)
#define RSL_ENC_ALG_A5(x) (x+1)
@@ -207,6 +221,9 @@
struct gsm_meas_rep meas_rep[6];
int meas_rep_idx;
+ /* table of neighbor cell measurements */
+ struct neigh_meas_proc neigh_meas[MAX_NEIGH_MEAS];
+
struct {
u_int32_t bound_ip;
u_int32_t connect_ip;
@@ -463,6 +480,19 @@
int send_mm_info;
struct {
int active;
+ /* Window RXLEV averaging */
+ unsigned int win_rxlev_avg; /* number of SACCH frames */
+ /* Window RXQUAL averaging */
+ unsigned int win_rxqual_avg; /* number of SACCH frames */
+ /* Window RXLEV neighbouring cells averaging */
+ unsigned int win_rxlev_avg_neigh; /* number of SACCH frames */
+
+ /* how often should we check for power budget HO */
+ unsigned int pwr_interval; /* SACCH frames */
+ /* how much better does a neighbor cell have to be ? */
+ unsigned int pwr_hysteresis; /* dBm */
+ /* maximum distacne before we try a handover */
+ unsigned int max_distance; /* TA values */
} handover;
/* layer 4 */