Random access satellite communication system using random numbers generated in a range variable with channel traffic

• US 5,434,847 A
• Filed: 02/25/1994
• Issued: 07/18/1995
• Est. Priority Date: 02/26/1993
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kou, Yukari
• Primary Examiner(s): MARCELO, MELVIN C
• Application Number:
  US08/202,353
• Time in Patent Office: 508 Days
• Field of Search: 370/17, 370/79, 370/85.2, 370/85.3, 370/85.6, 370/85.7, 370/94.1, 370/94.2, 370/95.1, 370/95.3, 370/97, 370/104.1, 370/110.1
• US Class Current: 370/252
• CPC Class Codes: H04B 7/212 Time-division multiple access [TDMA]
• CPC Class Codes: H04L 1/1809 Selective-repeat protocols
• CPC Class Codes: H04L 1/1887 Scheduling and prioritising arrangements

Abstract

In a satellite communications system comprising a central station and remote stations, each remote station sends a packet containing user data on a randomly determined slot of a forward satellite channel. If the packet is received by the central station, it sends traffic data and an acknowledgment signal. If the absence of acknowledgment signal is detected by the remote station, it generates a random number in a range determined by the traffic data and increments a count value indicating a number of instances where the acknowledgment signal is not returned. The packet containing the count value is retransmitted on a time slot determined by the random number. If an acknowledgment signal is received, the count value is reset to zero. The central station, on receiving a packet, generates an acknowledgment signal, and derives a sum of the total of packets received during a predetermined interval and the total of count values contained in such packets. The traffic data is derived from the sum and transmitted with the acknowledgment signal and host data on a backward satellite channel.

Claims

1. A satellite communications system including a central station and a plurality of remote stations for establishing a forward channel from each of said remote stations to said central station via a satellite and a backward channel from said central station to each of said remote stations via said satellite, said backward channel being divided into a plurality of frames and said forward channel being divided into frames corresponding to the frames of the backward channel, each of the frames of the forward channel being subdivided into slots,

each of said remote stations comprising:

means for transmitting a packet containing user data randomly on one of said slots;

means for receiving traffic data and an acknowledgment signal from said central station if said packet is received by the central station or receiving no acknowledgment signal if said packet is not received by the central station;

a random number generator capable of generating random numbers in a range determined by said traffic data, said random number generator being responsive to receipt of no acknowledgment signal for generating one of said random numbers;

means responsive to receipt of no acknowledgment signal for incrementing a count value;

means for retransmitting the packet containing the count value on a slot of the forward channel identified by the generated random number; and

means responsive to receipt of said acknowledgment signal for resetting said count value to zero,

said central station comprising;

means for receiving a packet from each remote station;

means for generating said acknowledgment signal in response to receipt of said packet;

means for deriving a sum of a total of the packets received during a predetermined interval and a total of the count values contained in said received packets;

means for deriving said traffic data from said sum; and

means for transmitting the acknowledgment signal and the traffic data on one of said frames of the backward channel together with host data.

2. A satellite communications system as claimed in claim 1, wherein said means for deriving said traffic data comprises means for comparing said sum total with threshold values respectively representing congestion levels of said forward channel and producing said traffic data representative of a congestion level of said forward channel.

3. A satellite communications system as claimed in claim 1, wherein said means for receiving said packet comprises means for detecting an error from the received packet and generating a signal indicating that the packet is validly received if substantially no error is detected therein, and said means for deriving a sum comprises means for counting said signal from said error detecting means to provide said total of the packets received during said predetermined interval.

4. In a satellite communications system including a central station and a plurality of remote stations for establishing a forward channel from each of said remote stations to said central station via a satellite and a backward channel from said central station to each of said remote stations via said satellite, said backward channel being divided into a plurality of frames and said forward channel being divided into frames corresponding to the frames of the backward channel, each of the frames of the forward channel being subdivided into slots, a method comprising the steps of:

a) transmitting a packet containing user data randomly on one of said slots from one of the remote stations;

b) receiving, at said remote station, traffic data and an acknowledgment signal from said central station if the packet is received by the central station or receiving no acknowledgment signal if the packet is not received by said central station;

c) if no acknowledgment signal is received by the step (b), generating a random number in a range determined by the traffic data;

d) incrementing a count value indicating a number of times the step (c) is repeated, and retransmitting the packet containing said count value on a slot of the forward channel determined by said random number;

e) repeating the steps (b) to (d); and

f) if said acknowledgment signal is received by the step (b), resetting said count value to zero;

g) receiving, at said central station, packets from said remote stations and generating acknowledgment signals for the received packets;

h ) deriving a sum of a total of the packets received by the step (g) during a predetermined interval and a total of the count values contained in the received packets;

i) deriving said traffic data from said sum; and

j) transmitting the acknowledgment signals, the traffic data and host data on one of said frames of the backward channel.

5. A method as claimed in claim 4, wherein the step (i) comprises comparing said sum total with threshold values respectively representing congestion levels of said forward channel and producing said traffic data representative of a congestion level of said forward channel.

6. A method as claimed in claim 4, wherein the step (g) comprises detecting an error from the received packet and generating a signal indicating that the packet is validly received if substantially no error is detected therein and the step (h) comprises counting said signal during said predetermined interval to provide said total of the packets.