Frequency hopping time-diversity communications systems and transceivers for local area networks

• US 5,448,593 A
• Filed: 07/24/1992
• Issued: 09/05/1995
• Est. Priority Date: 03/06/1984
• Status: Expired due to Fees

• Current Assignee: dbi Corp.
• Original Assignee: Cyplex Corporation
• Inventors: Hill, Lawrence W.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Le, Amanda T.
• Application Number:
  US07/920,110
• Time in Patent Office: 1,138 Days
• Field of Search: 375/10, 375/40, 375/98, 375/38, 375/109, 375/59, 375/8, 371/5.1, 371/5.2, 370/18, 370/92, 370/94.1, 370/60, 370/85.3, 370/93, 455/226.1, 455/226.2, 455/226.3
• US Class Current: 375/267
• CPC Class Codes: G05D 1/0265 using buried wires
• CPC Class Codes: G06F 11/076 by exceeding a count or rate limit, e.g. word- or bit count limit
• CPC Class Codes: H03G 3/001 Digital control of analog signals
• CPC Class Codes: H03G 3/002 Control of digital or coded signals H03G3/3089 take precedence
• CPC Class Codes: H04B 1/69 Spread spectrum techniques
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04B 1/715 Interference-related aspects
• CPC Class Codes: H04B 2001/7152 with means for suppressing interference
• CPC Class Codes: H04B 2001/71563 Acquisition
• CPC Class Codes: H04B 2203/5408 using protocols
• CPC Class Codes: H04B 2203/5416 by adding signals to the wave form of the power source
• CPC Class Codes: H04B 2203/5425 improving S/N by matching impedance, noise reduction, gain control
• CPC Class Codes: H04B 2203/5445 Local network
• CPC Class Codes: H04B 2203/5483 using coupling circuits
• CPC Class Codes: H04B 2203/5495 having measurements and testing channel
• CPC Class Codes: H04B 3/54 Systems for transmission via power distribution lines
• CPC Class Codes: H04B 3/56 Circuits for coupling, blocking, or by-passing of signals
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04B 7/12 Frequency diversity
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04L 1/02 : by diversity reception

Abstract

A system utilizing adaptive frequency-hopped spread spectrum modulation to communicate over AC power lines and other noisy communications channels is described. The system employs a modulation structure in which individual packets of data are transmitted with FSK modulation using two frequencies chosen from a larger set. An error coding system is used which provides a controlling microprocessor with data on the quality of reception at each transceiver in the network; this information is used to alter the gain of the receiver, the bit rate of the transmission, and the specific frequencies employed by the network, in real time, to optimize communication error rate. Messages are organized in packets. A Master transceiver, controlling network management, transmits channel control information to other transceivers on the network, enabling system synchronization, acquisition of an existing network by new subscribers, and changes to the bit rate and frequency set in use. Each transceiver comprises a frequency controlled carrier generator, appropriate data keying for the carrier, a pair of digital detectors each having a frequency controlled bandpass filter connected thereto, appropriate microprocessors for control and broad band coupling networks for coupling the transceiver to a communications channel, which may be an AC power line, a private line, the floor loop of an automatic guided vehicle system, or the like.

Claims

1. A communications system comprising at least one receiver employing automatic gain control for receiving binary coded parity checked information in successive packets;

said receiver comprising;

A) means for determining the bit error rate occurring in received packets by analyzing said packets for errors over a selected sample period of a plurality of successive sample periods; and

storing said rate;

B) means for comparing said bit error rate with the bit error rate in a sample period occurring before said selected sample period; and

C) means for changing the gain of the receiver in the same direction that it was changed previously when the current bit error rate is less than the previously measured bit error rate and for changing the gain in the opposite direction when the current bit error rate is greater than the previously measured bit error rate.

2. The system defined in claim 1 and

D) means for keeping the gain at the same setting for a predetermined number of successive ones of said sample periods after changing the gain in said opposite direction.

3. The system defined in claim 2 wherein said sample period is a number of packets received.

4. The system defined in claim 1 wherein said sample period is a number of packets received.

5. A communciations system as defined in claim 1 further comprising a transmitter and wherein binary coded information packets including error codes are transmitted from the transmitter to the receiver on at least one of a plurality of modulated frequencies and the receiver transmits to the transmitter an error signal when the receiver determines that a packet was received with an error;

said transmitter comprising;

A) means for setting the transmission bit rate at one of a plurality of bit rates between upper and lower limits;

B) means for maintaining a variable related to bit error rate (BRCNT), having upper and lower limits, and updated as follows, where (N-1) indicates the current BRCNT value and (N) indicates the new BRCNT value ##EQU2## and for decrementing the setting of said bit rate when the BRCNT reaches said upper limit and for incrementing the setting of said bit rate when said BRCNT reaches said lower limit; and

C) means for changing at least one frequency used in the next packet transmission when the BRCNT reaches said upper limit and the bit rate used in the error containing packet was the lowest bit rate available.

6. A communication system as defined in claim 5 comprising a plurality of slave modems each comprising a receiver substantially identical to said receiver and each connected to a host, said receiver further comprising:

A) means for receiving binary coded information packets on said plurality of modulated frequencies;

B) means for searching said frequencies for packets containing one of a plurality of master addresses and for only transmitting to its host packets containing said one master address.

7. A communication system as defined in claim 6 and

C) a master modem having a specific master address and comprising

a) means for searching said channels for and, disabling itself when, a packet is received containing said specific master modem address from another master.

8. A communication system as defined in claim 1 comprising a plurality of slave modems each comprising a receiver substantially identical to said receiver and each connected to a host, said receiver further comprising:

A) means for receiving binary coded information packets on said plurality of modulated frequencies;

B) means for searching said frequencies for packets containing one of a plurality of master addresses and for only transmitting to its host packets containing said one master address.

9. A communciations system comprising a transmitter and receiver wherein binary coded information packets including error codes are transmitted from a transmitter to a receiver on at least one of a plurality of modulated frequencies and the receiver transmits to the transmitter an error signal when the receiver determines that a packet was received with an error;

said transmitter comprising;

A) means for setting the transmission bit rate at one of a plurality of bit rates between upper and lower limits;

B) means for maintaining a variable related to bit error rate (BRCNT), having upper and lower limits, and updated as follows, where (N-1) indicates the current BRCNT value and (N) indicates the new BRCNT value ##EQU3## and for decrementing the setting of said bit rate when the BRCNT reaches said upper limit and for incrementing the setting of said bit rate when said BRCNT reaches said lower limit; and

C) means for changing at least one frequency used in the next packet transmission when the BRCNT reaches said upper limit and the bit rate used in the error containing packet was the lowest bit rate available.

10. A communication system as defined in claim 9 wherein said receiver utilizes integrate and dump bit detection.

11. A communication system comprising a plurality of slave modems each connected to a host comprising:

A) means for receiving binary coded information packets on a plurality of communication channels;

B) means for searching said channels for packets containing one of a plurality of master addresses and for only transmitting to its host packets containing said master address; and

,

C) a master modem having a specific master address and comprising

a) means for searching said channels for and, disabling itself when, a packet is received containing said specific master modem address from another master.