An apparatus for controlling hand-off in a spread-spectrum-CDMA-communications system, for radio devices moving from one cell to another, with each cell having a base station transmitting spread spectrum signals with generic-chip-code signals. A radio device includes a cellular antenna, matched filters, and detectors for detecting generic-chip-code signals embedded in spread-spectrum-communications signals. A comparator generates a comparison signal by comparing the relative time of arrival of a second detected signal with a first detected signal. A receiver-message-chip-code generator generates a replica of the message-chip-code signal, and a message mixer despreads the spread-spectrum-communications signal. A synchronization circuit synchronizes the receiver-message-chip-code generator to the first generic-chip-code signal for receiving the first spread-spectrum-communications signal or to the second generic-chip-code signal for receiving the second spread-spectrum communications signal, depending on a threshold. A control unit switches transmitting the message data, embedded in the first spread-spectrum-communications signal from the first base station, to the second spread-spectrum-communications signal transmitted from the second base station. Hand-off from an analog base station to a second base station utilizing spread spectrum is also possible.
RELATED PATENTS
This patent issues from a continuation-in-part patent application, whose parent patent application has Ser. No. 07/727,617, with a filing date of Jul. 10, 1991, entitled, SPREAD SPECTRUM CELLULAR HAND-OFF APPARATUS AND METHOD, which is now issued U.S. Pat. No. 5,179,571. All matter from the parent patent application is incorporated herein by reference, and benefit of earlier filing date of the parent patent application is claimed pursuant to 35 U.S.C. .sctn.120.
This invention is related to the disclosures in U.S. patent application Ser. No. 07,622,235, having filing date of Dec. 14, 1990, entitled, SPREAD SPECTRUM CDMA COMMUNICATIONS SYSTEM by Donald L. Schilling; U.S. patent application Ser. No. 07/614,816, having filing date of Nov. 16, 1990, and entitled ADAPTIVE POWER CONTROL FOR A SPREAD SPECTRUM TRANSMITTER by Donald L. Schilling, which is now U.S. Pat. No. 5,093,840, with an issue date of Mar. 3, 1992; U.S. patent application Ser. No. 07/614,827, having filing date of Nov. 16, 1990, and entitled SPREAD SPECTRUM MULTIPATH RECEIVER APPARATUS AND METHOD by Donald L. Schilling, which is now U.S. Pat. No. 5,081,643, with an issue date of Jan. 14, 1992; and, U.S. patent application Ser. No. 07/626,109, having filing date of Dec. 14, 1990, and entitled SPREAD SPECTRUM COMMUNICATIONS SYSTEM AND METHOD by Donald L. Schilling; which are all incorporated herein by reference.
With respect to a direct sequence, code division multiple access spread spectrum transmitter, symbol information relating to dedicated/common channels (such as the traffic or control channels) is spread to generate a plurality of corresponding dedicated/common channel intermediate signals. These intermediate signals are then summed to generate an output signal that is scrambled by a selected scrambling code. Symbol information relating to acquisition-related channels (such as synchronization information or the pilot or long code group code channels) is also spread to generate a plurality of corresponding acquisition-related intermediate signals. These acquisition-related intermediate signals are then selectively added to the scrambled output signal producing a downlink signal for multi-channel transmission over a communications medium sharing one transmission communications frequency.
The present invention realizes a rapid and efficient cell search and small-size instrument for an asynchronous DS-CDMA cellular system. This cell search detects the correlation between the received signal and the short code of the control channel, and matched filter 22 detects the maximum electric power correlation peak location. Next, using correlators 28-1 to 28-n which are parallelly set in a plurality for RAKE processing with plurality, identifies the long code that is set in the system with the detected long code timing. After the long code is synchronized, a multipath signal is received using 28-1 to 28-n, and the data is judged by RAKE processing. When peripheral cell search is executed, after long code timing is detected by using matched filter 22, the long code of the candidate peripheral cell is designated using the same matched filter. Handover is safely realized by receiving the signal from the connected base station by correlators 28-1 to 28-n, and the base station signal through handover by 22.
An independent wideband pilot channel transmitter is located in each cell of a frequency division multiple access communications system which is adjacent to a code division multiple access communications system. Operation of the independent wideband pilot channel transmitter is controlled by a mobile switching center of the code division multiple access communications system. Wideband pilot channel broadcasts from the independent wideband pilot channel transmitters are then monitored by dual mode mobile stations in accordance with mobile assisted handoff (MAHO) procedures for the purpose of identifying target cells in the frequency division multiple access communications system which are suitable for handoff.
A mobile station, and a method for making a handover in a CDMA cellular radio system, which includes in each cell at least one base station connected to the mobile stations in the cell. The connection includes both a traffic channel and one or more control channels. The transmissions of the base stations are not synchronized with each other. A mobile station, after having established a simultaneous connection with two or more of the base stations while making a handover, transmits to the base stations using the same spreading code. The signals received by the base stations are combined in a base station controller, or the like. The base stations with which the mobile station communicates simultaneously, transmit to the mobile station each using a different spreading code. The mobile station receives and demodulates each of the signals, transmitted with different spreading codes, by a different rake receiving unit independent of the other units, each receiving unit being synchronized with the signal from the base station it is receiving. The mobile station combines the signals it has received from the base stations and demodulated by using its plural rake receiving units.
A virtual pilot channel generating apparatus and its operating method for supporting effective hand-off between frequencies in a CDMA mobile communications system, in which, when base stations A and B use frequency channels different from each other and a user moves from the base station A to base station B, pilot information the same as CDMA allocation frequency used in the base station A is supplied to the hardware of the base station B, and the hardware of the base station B transmits a virtual pilot channel identical to CDMA allocation channel used in the base station A, to allow the user's mobile to simultaneously monitor power intensities of the pilot channels of the base stations A and B, initiating smooth hand-off.
