2. section (Continued) 6 Call Layer 3 Processing

2.6.6.1 Overview

2.6.6.1.1 Types of Handoff

• Soft Handoff: A handoff in which the mobile station commences communications with a new base station without interrupting communications with the old base station. Soft handoff can only be used between CDMA Channels having identical Frequency Assignments. Soft handoff provides diversity of Forward Traffic Channels and Reverse Traffic Channel paths on the boundaries between base stations.

• CDMA-to-CDMA Hard Handoff: A handoff in which the mobile station is transitioned between disjoint sets of base stations, different band classes, different Frequency Assignments, or different frame offsets.

• CDMA-to-Analog Handoff: A handoff in which the mobile station is directed from a CDMA traffic channel to an analog voice channel.

The mobile station shall support soft handoffs on the same Frequency Assignment (see 2.6.6.2.7). The mobile station shall support CDMA-to-CDMA hard handoffs between band classes on which it supports CDMA operation (see 2.6.6.2.8). The mobile station shall support CDMA-to-Analog handoffs from band classes on which it supports CDMA operation to band classes on which it supports analog operation (see 2.6.6.2.9).

2.6.6.1.2 Pilot Sets

The mobile station searches for pilots on the current CDMA Frequency Assignment to detect the presence of CDMA Channels and to measure their strengths. When the mobile station detects a pilot of sufficient strength that is not associated with any of the Forward Traffic Channels assigned to it, it sends a Pilot Strength Measurement Message or an Extended Pilot Strength Measurement Message to the base station. The base station can then assign a Forward Traffic Channel associated with that pilot to the mobile station and direct the mobile station to perform a handoff.

The pilot search parameters and the rules for Pilot Strength Measurement Message or Extended Pilot Strength Measurement Message transmission are expressed in terms of the following sets of pilots:

• Active Set: The pilots associated with the Forward Traffic Channels assigned to the mobile station.

• Candidate Set: The pilots that are not currently in the Active Set but have been received by the mobile station with sufficient strength to indicate that the associated Forward Traffic Channels could be successfully demodulated.

• Neighbor Set: The pilots that are not currently in the Active Set or the Candidate Set and are likely candidates for handoff.

• Remaining Set: The set of all possible pilots in the current system on the current CDMA Frequency Assignment, excluding the pilots in the Neighbor Set, the Candidate Set, and the Active Set. This set of possible pilots consists of pilots whose pilot PN sequence offset indices are integer multiples of PILOT_INC_s.

The base station may direct the mobile station to search for pilots on a different CDMA frequency to detect the presence of CDMA Channels and to measure their strengths. The mobile station reports the results of the search to the base station using the Candidate Frequency Search Report Message. Depending upon the pilot strength measurements reported in the Candidate Frequency Search Report Message, the base station can direct the mobile station to perform an inter-frequency hard handoff.

The pilot search parameters are expressed in terms of the following sets of pilots on the CDMA Candidate Frequency:

• Candidate Frequency Neighbor Set: A list of pilots on the CDMA Candidate Frequency.

• Candidate Frequency Search Set: A subset of the Candidate Frequency Neighbor Set that the base station may direct the mobile station to search.

2.6.6.2 Requirements

2.6.6.2.1 Pilot Search

Search performance criteria are defined in TIA/EIA-98-C and ANSI J-STD-018.

This search shall be governed by the following:

• Active Set and Candidate Set: The search procedures for pilots in the Active Set and Candidate Set shall be identical. The search window size¹⁵ for each pilot in the Active Set and Candidate Set shall be the number of PN chips specified in Table 2.6.6.2.1-1 corresponding to SRCH_WIN_A_s. The mobile station should center the search window for each pilot of the Active Set and Candidate Set around the earliest arriving usable multipath component of the pilot. If the mobile station receives a value greater than or equal to 13 for SRCH_WIN_A_r, it may store and use the value 13 in SRCH_WIN_A_s.

SRCH_WIN_A SRCH_WIN_N SRCH_WIN_NGHBR SRCH_WIN_R CF_SRCH_WIN_N	window_size (PN chips)	SRCH_WIN_A SRCH_WIN_N SRCH_WIN_NGHBR SRCH_WIN_R CF_SRCH_WIN_N	window_size (PN chips)
0	4	8	60
1	6	9	80
2	8	10	100
3	10	11	130
4	14	12	160
5	20	13	226
6	28	14	320
7	40	15	452

SRCH_OFFSET_NGHBR CF_SRCH_OFFSET_NGHBR	Offset ( PN chips)
0	0
1	window_size/2
2	window_size
3	3  window_size /2
4	- window_size /2
5	- window_size
6	-3  window_size /2
7	Reserved

• Neighbor Set: If SRCH_WIN_NGHBR_INCL_s is equal to ‘1’, the search window size for each pilot in the Neighbor Set shall be the number of PN chips specified in Table 2.6.6.2.1-1, corresponding to SRCH_WIN_NGHBR_s associated with the pilot being searched. If SRCH_WIN_NGHBR_INCL_s is equal to ‘0’, the search window size for each pilot in the Neighbor Set shall be the number of PN chips specified in Table 2.6.6.2.1-1 corresponding to SRCH_WIN_N_s. If SRCH_OFFSET_INCL_s is equal to ‘1’, the search window offset for each pilot in the Neighbor Set shall be the number of PN chips specified in Table 2.6.6.2.1-2, corresponding to SRCH_OFFSET_NGHBR_s associated with the pilot being searched. If SRCH_OFFSET_INCL_s is equal to ‘0’, the search window offset for each pilot in the Neighbor Set shall be zero PN chip. The mobile station should center the search window for each pilot in the Neighbor Set around the pilot’s PN sequence offset plus the corresponding search window offset, using timing defined by the mobile station’s time reference (see TIA/EIA/IS-2000-2). If SEARCH_PRIORITY_INCL_s is equal to ‘1’, the mobile station should use SEARCH_PRIORITY_s for the corresponding pilot to schedule its neighbor search. If the mobile station supports hopping pilot beacons and the TIMING_INCL field of the NGHBR_REC for the corresponding pilot is equal to ‘1’, then the mobile station shall use the information included in the NGHBR_TX_OFFSET, NGHBR_TX_DURATION, and NGHBR_TX_PERIOD fields of the NGHBR_REC for the corresponding pilot to schedule the time for searching the neighbor. If ADD_PILOT_REC_INCL field of the NGHBR_REC for the corresponding pilot is equal to ‘1’, the mobile station shall use the information included in the NGHBR_PILOT_REC field for searching the neighbor.

• Remaining Set: The search window size for each pilot in the Remaining Set shall be the number of PN chips specified in Table 2.6.6.2.1-1 corresponding to SRCH_WIN_R_s. The mobile station should center the search window for each pilot in the Remaining Set around the pilot’s PN sequence offset, using timing defined by the mobile station’s time reference (see TIA/EIA/IS-2000-2). The mobile station should only search for Remaining Set pilots whose pilot PN sequence offset indices are equal to integer multiples of PILOT_INC_s.

• Candidate Frequency Search Set: If CF_SRCH_WIN_NGHBRN_INCL_s is equal to ‘1’, the search window size for each pilot in the Candidate Frequency Search set shall be the number of PN chips specified in Table 2.6.6.2.1-1, corresponding to SRCH_WIN_NGHBR_s associated with the pilot being searched. If CF_SRCH_WIN_NGHBR_INCL_s is equal to ‘0’, the search window size for each pilot in the Candidate Frequency Search Set shall be the number of PN chips specified in Table 2.6.6.2.1-1 corresponding to CF_SRCH_WIN_N_s. If CF_SRCH_OFFSET_INCL_s is equal to ‘1’, the search window offset for each pilot in the Candidate Frequency Search Set shall be the number of PN chips specified in Table 2.6.6.2.1-2, corresponding to SRCH_OFFSET_NGHBR_s associated with the pilot being searched. If CF_SRCH_OFFSET_INCL_s is equal to ‘0’, the search window offset for each pilot in the Candidate Frequency Search Set shall be zero PN chip. The mobile station should center the search window for each pilot in the Candidate Frequency Search Set around the pilot’s PN sequence offset plus the corresponding search window offset using timing defined by the mobile station’s time reference (see TIA/EIA/IS-2000-2). If CF_SEARCH_PRIORITY_INCL_s is equal to ‘1’, the mobile station should use SEARCH_PRIORITY_s associated with each pilot to schedule a search of its Candidate Frequency Search Set.