Đang chuẩn bị liên kết để tải về tài liệu:
Code Division Multiple Access (CDMA) phần 7

Với BFSK và không kết hợp tiếp nhận, xác suất của lỗi trong trường hợp không có va chạm là [22] Po = 1 Eb 1 điểm kinh nghiệm - 2 2 N0 (2,90) Bây giờ, với mã số nhảy ngẫu nhiên độc lập, xác suất của ít nhất | 106 CODE DIVISION MULTIPLE ACCESS CDMA set and into its candidate set. The mobile then requests a hand-off to that cell. 2 If the cell has sufficient resources the mobile switching center will send a message to the base station and the mobile to begin a hand-off. 3 The mobile moves the pilot to its active set and completes hand-off. As long as the signal strength remains above a drop threshold T_DROP the signal will remain in its active set. The mobile then communicates simultaneously with all base stations in its active set. Most CDMA systems support at least three-way soft hand-off with some supporting up to six-way soft hand-off. 4 When the pilot strength drops below the drop threshold the mobile begins a hand-off drop timer. 5 When the hand-off drop timer expires the mobile sends a hand-off message to the base station. 6 The base station then acknowledges receipt of the hand-off request by sending its own hand-off message. 7 Finally the mobile terminates its connection and moves the pilot to its neighbor set. Besides macro-diversity soft hand-off ensures that a mobile is always communicating with the strongest base station in its view. In classic hard hand-off techniques the hysteresis effect ensures that a mobile does not ping-pong between base stations. However in doing so the mobile is not always communicating with the strongest base station. This is tolerable although not optimal in FDMA TDMA systems but is a problem in CDMA systems since it means that the strongest base station is actually causing substantial interference. Soft hand-off avoids this. Finally a distinction between soft hand-off between two base stations and soft hand-off between two sectors of the same base station must be explained. The latter is usually termed softer hand-off. Soft and softer hand-off look identical to the mobile station since it cannot distinguish between two cells and two sectors from the same cell. However it makes a difference on uplink performance in softer hand-off .