Space diversity system in PCM-TDMA telecommunication system using stationary communication satellite

• US 4,052,670 A
• Filed: 12/23/1975
• Issued: 10/04/1977
• Est. Priority Date: 12/24/1974
• Status: Expired due to Term

• Current Assignee: Kokusai Denshin Denwa KK (KDDI Corporation)
• Original Assignee: Kokusai Denshin Denwa KK (KDDI Corporation)
• Inventors: Saito, Hideki, Ogawa, Akira, Watanabe, Tatsuo, Yamaguchi, deceased, Masahisa
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Chin, Tommy P.
• Application Number:
  US05/643,708
• Time in Patent Office: 651 Days
• Field of Search: 325/2, 325/4, 325/5, 325/6, 325/58, 325/56, 325/301, 325/302, 325/303, 325/304, 325/305, 325/306, 178/69.5 R, 179/15 BS
• US Class Current: 370/324
• CPC Class Codes: H04B 7/0817 with multiple receivers and antenna path selection
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04B 7/212 Time-division multiple access [TDMA]

Abstract

A space diversity PCM-TDMA telecommunication system using a stationary communication satellite, in which fixed delay circuits are respectively inserted in the sending side and the receiving side of one route at a control equipment, while variable delay circuits are inserted in the sending side and the receiving side of the other route at the control equipment, so that electrical length of one route from the satellite to the control equipment may be the same as that of the other route from the satellite to the control equipment through the route including connection links between the two sites. Diversity switching can be performed with no duplication and lack of signals in accordance with the above construction.

Claims

1. A space diversity system with at least two signal routes in a PCM-TDMA telecommunication system utilizing a communication satellite generally stationary with respect to ground stations of the system, comprising;

signal conversion circuits each inserted in the receiving side of a respective one of said at least two signal routes for converting the received PCM signals of burst mode at each route into PCM signals synchronized with consecutive clock pulses of a respective ground station for each route,

phase difference detection means connected to said signal conversion circuits for establishing an arrival time difference between said PCM signals of said routes,

fixed delay circuits inserted in at least one of said signal routes for correcting a fixed delay difference between said routes,

variable delay circuits inserted in at least a remaining one of said signal routes and responsive to the output of said phase difference detection means for correcting the deviation of said arrival time difference between said PCM signals of said routes which occurs in accordance with any movement of said satellite, thereby equalizing respective electrical lengths of said routes to one another; and

switchover means connected to said signal routes for selecting one of said signal routes in accordance with the quality of the signals received at each route.

2. A space diversity system according to claim 1, in which said signal conversion circuits each comprise a clock detection circuit to detect the presence of recovered burst clock pulses from the received PCM signals of burst mode, a write clock generator to generate write clock pulses, synchronized with said regenerated burst clock pulses, when said clock detection circuit detects said recovered clock pulses, a memory to temporarily store said received PCM signal series under the control of said write clock pulses, a continuous clock pulse generator to generate continuous clock pulses of a repetition frequency approximately equal to the repetition frequency of said recovered burst clock pulses, a read clock generator to generate read clock pulses synchronized with said continuous clock pulses when said clock detection circuit detects said recovered clock pulses, and a memory read circuit to read data stored in said memory under the control of said read clock pulses, whereby said received PCM signal series of burst mode can be converted to an output signal series synchronized with said continuous clock pulses.

3. In a space diversity satellite PCM-TDMA telecommunication system of the type including at least a pair of ground antennas located at separate sites and a satellite generally stationary with respect to the ground antennas, each of the ground antennas and the satellite defining therebetween a respective space signal channel through which signals are transmitted between the satellite and the ground antennas, the satellite including a transmitter for transmitting PCM signals in a burst mode to the ground antennas, and at least two receivers each connected to a respective one of the ground antennas for receiving signals transmitted from the satellite, the improvement which comprises:

a respective signal conversion means connected to each of the receivers for converting received PCM burst mode signals, transmitted from the satellite through the respective space channels, into synchronized PCM signals synchronized with respective clock pulse trains;

phase difference detecting means connected to receive the respective synchronized PCM signals from the respective signal conversion means for developing phase difference signals representative of phase differences between the respective synchronized PCM signals and which phase differences are representative of the difference between the arrival times of PCM signals transmitted from the satellite and received at respective ones of the ground receiving antennas;

first delay means connected to receive the respective synchronized PCM signals from one of said signal conversion means for delaying the respective synchronized PCM signals by a fixed delay equal to a fixed delay in arrival time of the PCM burst mode signals, transmitted from the satellite through the space transmission channel corresponding to said one of said signal conversion means, after the arrival time of the PCM burst mode signals transmitted from the satellite through the space transmission channel corresponding to the other of said signal conversion means, thereby to correct the fixed delay;

second delay means connected to receive the respective synchronized PCM signals from the other one of said signal conversion means, and responsive to the output of said phase difference detecting means for delaying the synchronized PCM signals in dependence on the phase difference signals for correcting a variation of the arrival time difference between the arrival times of the PCM burst mode signals received at the ground station antennas which occurs in response to motion of the satellite relative to the ground antennas; and

signal selecting means, connected to receive the delayed synchronized PCM signals developed by said first delay means corresponding to one of the space channels and connected to receive the delayed synchronized PCM signals developed by said second delay means corresponding to the other of the space channels, and operable for selecting one of the delayed synchronized PCM signals in accordance with the signal quality of the PCM signals transmitted through the respective space signal channels.