Scanning method for receiving a transmission in a communication system with slow frequency hopping and coding

A decentralized communication method for communicating a packet of data between a plurality of stations using frequency hopping in a predetermined channel sequence of N radio frequencies, said communication method comprising the steps of:

• (a) in an arbitrary transmitting station, transmitting a packet including the steps of
• (a)(i) encoding and arranging said packet into a plurality of N segments according to a predetermined protocol and a predetermined encoding in which the data in said packet is recoverable even if a number e of said N segments are erased, and
• (a)(ii) transmitting said N segments sequentially by hopping through said predetermined channel sequence of N radio frequencies, so that a first segment is transmitted on a first channel, a second segment is transmitted on a second channel, and so forth until the N.sup.th sediment is transmitted on an N.sup.th channel;
• and
• (b) in a plurality of receiving stations that are unsynchronized with said transmitting station, performing the steps of
• (b)(i) scanning a subset of frequencies of said N radio frequencies, said subset including a first plurality p (p<N) of frequencies in said predetermined channel sequence wherein a scan time for each frequency of said subset is substantially less than the time necessary to receive a segment,
• (b)(ii) testing for the presence of a transmission on one of said p scanned frequencies,
• (b)(iii) if a transmission is detected on one of said p scanned frequencies, then synchronizing the receiving station with the transmitted packet, then receiving a segment in the frequency in which the transmission is first detected, hopping to the next frequency in the predetermined channel sequence and receiving a segment on that channel, and continuing until the N.sup.th segment has been received, and
• (b)(iv) decoding said received segments to recover the data packet.

A scanning and receiving circuit for receiving a packet that has been arranged by a transmitting station according to a predetermined protocol having N segments including a predetermined encoding in which the data in said packet is recoverable even if a number e of said N segments are erased, said segments being transmitted using N frequencies in a predetermined channel sequence, said scanning and receiving circuit comprising:

• an antenna for receiving said plurality of frequencies;
• a radio frequency (RF) modem coupled to said antenna, including
• a frequency synthesizer for producing a plurality of RF frequencies,
• a RF control unit coupled to the frequency synthesizer for selecting a radio frequency, said control unit including means for controlling the frequency synthesizer so that it serially scans p (1.ltoreq.p.ltoreq.N) frequencies of the N frequencies in said predetermined channel sequence in substantially less time than the time necessary to receive a segment;
• and
• a RF receiver including a detection circuit for testing each frequency as it is scanned for the existence of a transmission and a circuit responsive to said detection circuit for controlling the RF receiver and the RF frequency synthesizer to synchronize with the transmitted packet and to receive the detected segment and following transmitted segments.

A frequency hopping communication unit for an unsynchronized station in a Local Area Network (LAN) that receives data and commands on a system bus, said frequency hopping communication unit comprising:

• an antenna;
• a radio frequency (RF) modem coupled to said antenna, including
• a frequency synthesizer for producing a plurality of RF frequencies,
• a RF transmitter,
• a RF receiver, and
• a RF control unit coupled to said RF transmitter and RF receiver, said RF control unit also coupled to the frequency synthesizer for selecting a radio frequency, said RF control unit including control means for controlling the frequency synthesizer so that it serially scans a selected number of frequencies in substantially less time than the time necessary to receive a segment;
• a data bus coupled to the RF modem for supplying data to the transmitter and receiving data front the receiver;
• and
• a LAN controller coupled to the RF modem and the data bus, said LAN controller comprising
• control logic coupled to the RF control unit for supplying control information thereto and for receiving status information therefrom, and
• a protocol engine coupled to receive data and commands from the system bus, said protocol engine also coupled to the control logic and the data bus, said protocol engine for arranging said packet according to a predetermined protocol having N segments and a predetermined protocol having N segments including a predetermined encoding in which the data in said packet is recoverable even if a number e of said N segments are erased, said protocol engine also for supplying the segments to the RF transmitter through the data bus and commands to the control logic.

In a decentralized communication system for communicating between two or more of a plurality of unsynchronized stations, a method for detecting and receiving a packet of data transmitted by an arbitrary transmitting station of said plurality of stations using frequency hopping in a predetermined channel sequence of N radio frequencies including a first p (p<N) frequencies, in which said transmitting station encodes and arranges the packet into a plurality of N segments including a first p (p<N) segments each having a corresponding preamble time length t.sub.1, comprising the steps of:

• (a) in an arbitrary receiving station that is unsynchronized with said transmitting station, scanning and testing said first p frequencies in a second time period t.sub.2 that is less than the preamble time length t.sub.1 ;
• (b) if a transmission is detected on a first one of said p frequencies, then performing a receiving step (c), otherwise returning to step (a);
• and
• (c) if a transmission is detected in the step (a), receiving the segment associated with said first one of said p frequencies, hopping to the next frequency in the predetermined channel sequence and receiving a segment on that channel, and continuing to hop and receive until the N.sup.th segment has been received.