US 5,206,881 AGranted

Wireless local area network

AssigneeTelesystems SLW Inc.

InventorsSteven Messenger, Tommy Tsoulogia

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Abstract

In a wireless local area network in which data packets are spread spectrum encoded, method and apparatus are provided for determining phase values that synchronize noise codes at network stations with received data packets. A synchronizing packet is first transmitted from a source station to various network stations. Each network station performs a wide-range search for a phase value that synchronizes the noise code of the station with the synchronizing packet. Thereafter, each network station performs narrow-range searches for phase values synchronizing the noise code of the station with subsequently received network packets. The stations switch to the wide-range search mode whenever a synchronizing phase angle has not been detected for predetermined period of time and switch to a narrow-range search mode whenever a synchronizing phase angle is detected. In a polled local area network, polling packets generated by a base station serve as synchronizing packets, and the base station is adapted to perform only narrow-range searches. Packets with shorter synchronization headers can be used thereby improving data transfer rates.

Claims23

Dependent claims

In a local area network comprising a plurality of stations each adapted to generate a PN code common to the stations, to transmit packets spread spectrum encoded with the PN code and to decode packets by combining the packets with the PN code, a method of determining phase values that synchronize the PN code of a first of the stations with a data packet transmitted through air by a second station to the first station, comprising:

transmitting from any one of the stations through air to the other stations a synchronizing packet direct sequence spread spectrum encoded with the PN code of the one station, the transmission of the synchronizing packet occurring before transmission of the data packet of the second station;
adjusting the phase of the PN code of each of the other stations prior to transmission of the data packet by the second station to a phase value synchronizing the phase of the PN code of the station with the phase of the transmitted synchronizing packet, the adjusting of the phase at each of the other stations comprising producing phase-shifted PN codes corresponding to the PN code of the station shifted in phase according to different phase values, combining the transmitted synchronizing packet with the phase-shifted PN codes to produce signals and detecting from the signals the synchronizing phase value;
searching at the first station for a phase value which synchronizes the PN code of the first station with the data packet, the searching at the first station comprising:
a. setting predetermined upper and lower bounds for a restricted set of phase values corresponding to the phase of the synchronizing packet,
b. selecting different phase values for the PN code of the first station from the restricted set,
c. producing phase-shifted PN codes corresponding to the PN code of the first station shifted in phase according to each of the phase values selected from the restricted set of phase values,
d. combining the phase-shifted PN codes with the data packet to produce signals each corresponding to a different phase value selected from the restricted set,
e. detecting from the signals a phase value which synchronizes the PN code with the data packet.

5 more elements

A method of determining phase values that synchronize a PN code generated at a network station of a local area network with temporally spaced-apart packets transmitted through the air by a source station, the method comprising:

generating the PN code at the source station and spread spectrum encoding each of the temporally spaced-apart packets at the source station prior to transmission by combining each of the packets with the PN code of the source station phase-shifted to a substantially constant preset phase value;
performing a wide-range search for a phase value synchronizing the PN code of the network station with a first of the packets, the wide-range search comprising
a. repeatedly selecting different phase values for the PN code of the network station from a relatively exhaustive set of phase values;
b. producing phase-shifted PN codes corresponding to the PN code of the network station shifted in phase according to each of the selected phase values;
c. combining the phase-shifted PN codes with the first packet to produce signals each corresponding to a different phase value selected from the relatively exhaustive set;
d. detecting from the signals a phase value which synchronizes the PN code of the network station with the first received packet;
performing a narrow-range search for phase values synchronizing the PN code of the network station with each of the temporally spaced-apart packets succeeding the first packet, the narrow-range search comprising
a. selecting different phase values for the PN code of the network station from a restricted set of phase values with predetermined upper and lower bounds corresponding to a phase value which synchronized the PN code of the network station with an immediately preceding one of the packets;
b. producing phase-shifted PN codes corresponding to the PN code of the network station shifted in phase according to each of the phase values selected from the restricted set;
c. combining the phase-shifted PN codes with a current one of the packets to produce signals each corresponding to a different phase value selected from the restricted set;
d. detecting from the signals a phase value of the restricted set which synchronizes the PN code of the network station with the current data packet.

8 more elements

A method of determining phase values that synchronize a PN code generated at a network station of a local area network with temporally spaced-apart network packets transmitted through air and received by the network station, each network packet being direct sequence spread spectrum encoded with the PN code, the method comprising:

inserting a predetermined indicator into a trailing portion of each of the network packets prior to encoding and transmission of the network packet;
searching in either a wide-range search mode or a narrow-range search mode for phase values synchronizing the PN code of the network station with each of the network packets;
the wide-range search mode comprising
a. repeatedly selecting different phase values for the PN code of the network station from a relatively exhaustive set of phase values;
b. producing phase-shifted PN codes corresponding to the PN code shifted in phase according to each of the phase values selected from the relatively exhaustive set;
c. combining the phase-shifted PN codes with a currently received one of the network packets to produce signals each corresponding to a different phase value selected from the relatively exhaustive set;
d. detecting from the signals corresponding to phase values selected from the relatively exhaustive set a phase value which synchronizes the PN code of the network station with the currently received network packet including decoding at least a portion of the currently received network packet by combining the packet portion with the PN code phase shifted according to the synchronizing phase value and detecting presence of the indicator in the decoded packet portion;
the narrow-range search mode comprising
a. selecting different phases values for the PN code of the network station from a restricted set of phase values having predetermined upper and lower bounds corresponding to a phase value that synchronized the PN code of the network station with an immediately preceding one of the received network packets;
b. producing phase-shifted PN codes corresponding to the PN code of the network station shifted in phase according to each of the phase values selected from the restricted set;
c. combining the phase-shifted PN codes with a currently received one of the network packets to produce signals each corresponding to a different phase value selected from the restricted set;
d. detecting from the signals corresponding to phase values selected from the restricted set a phase value which synchronizes the PN code of the network station with the currently received network packet including decoding at least a portion of the currently received network packet by combining the packet portion with the PN code phase shifted according to the synchronizing phase value and detecting presence of the indicator in the decoded packet portion;
switching from the wide-range search mode to the narrow-range search mode in response to detection of the indicator in a received network packet;
switching from the narrow-range search mode to the wide-range search mode whenever a predetermined period of time has expired from detection of the indicator in a received network patent.

11 more elements

In a local area network, apparatus for use in processing temporally spaced-apart network packets transmitted through air and direct sequence spread spectrum encoded with a predetermined PN code, the apparatus comprising:

means for generating the PN code;
means for receiving and decoding the network packets, the receiving and decoding means comprising means for adjusting the phase of the PN code of the apparatus to a phase value which synchronizes the PN code of the apparatus with each of the network packets and means for combining the phase-adjusted PN code with each packet to spread spectrum decode the packet, the phase adjusting means comprising means for searching in either a wide-range search mode or a narrow-range search mode for phase values synchronizing the generated PN code with the packets;
the searching means comprising
a. means for selecting different phase values for the PN code of the apparatus from a set of phase values,
b. means for producing phase-shifted PN codes corresponding to the PN code of the apparatus shifted in phase according to each of the selected phases,
c. means for combining the phase-shifted PN codes with a currently received one of the packets to produce signals each corresponding to a different phase value selected from the set,
d. means for detecting from the signals a phase value which synchronizes the PN code with the currently received packet;
the searching means being adapted in the wide-range search mode repeatedly to select the different phases values for the PN code of the apparatus from a relatively exhaustive set of phase values;
the searching means being adapted in the narrow-range search mode to select the different phases for the PN code of the apparatus from a restricted set of phase values having predetermined upper and lower bounds corresponding to a phase value that synchronized the PN code of the apparatus with an immediately preceding one of the received packets.

6 more elements

A polled local area network comprising:

network stations including a base station and a plurality of polled stations polled by the base station;
each of the network stations comprising
a. means for generating a PN code common to the network stations,
b. means for encoding and transmitting packets through air, the encoding means including means for direct sequence spread spectrum encoding each packet prior to transmission with the PN code of the network station;
c. means for receiving and decoding each packet transmitted through air to the network station and direct sequence spread spectrum encoded with the PN code, the receiving and decoding means comprising means for adjusting the phase of the PN code of the network station to a phase value which synchronizes the PN code of the network station with the received packet and means for combining the phase-adjusted PN code with the received packet to spread spectrum decode the received packet, the phase adjusting means comprising means for searching for phase values synchronizing the PN code of the network station with the received packet;
the searching means of each of the polled stations being adapted to search in either a wide-range search mode or a narrow-range search mode for a phase value synchronizing the PN code of the polled station with polling packets transmitted by the base station and spread spectrum encoded with the PN code of the base station, the searching means of each of the polled stations comprising means for
a. selecting different phase values for the PN code of the polled station from a set of phase values;
b. producing phase-shifted PN codes corresponding to the PN code of the polled station shifted in phase according to each of the selected phases;
c. combining the phase-shifted PN codes with a currently received polling packet to produce signals each corresponding to a different phase value selected from the set of phase values;
d. detecting from the signals a phase value synchronizing the PN code of the polled station with the currently received polling packet;
the searching means of each of the polled stations being adapted in the wide-range search mode repeatedly to select the different phases values for the PN code of the polled station from a relatively exhaustive set of phase values;
the searching means of each of the polled stations being adapted in the narrow-range search mode to select the different phases values for the PN code of the polled station from a restricted set of phase values having predetermined upper and lower bounds corresponding to a phase value that synchronized the PN code of the apparatus with an immediately preceding one of the polling packets received by the polled station;
the searching means of each of the polled stations being adapted to switch from the wide-range search mode to the narrow-range search mode in response to detection of a phase value synchronizing the PN code of the polled station with a polling packet and to switch from the narrow-range search mode to the wide range search mode whenever a predetermined period of time has expired from detection of a phase value synchronizing the PN code of the polled station with a polling packet.

10 more elements

A polled local area network comprising:

network stations including a base station and a plurality of polled stations;
each of the network stations comprising
a. means for generating a PN code common to the network stations,
b. means for encoding and transmitting packets through air, the encoding means including means for direct sequence spread spectrum encoding each packet prior to transmission with the PN code of the network station;
c. means for receiving and decoding each packet transmitted through air to the network station and direct sequence spread spectrum encoded with the PN code, the receiving and decoding means comprising means for adjusting the phase of the PN code of the network station to a phase value which synchronizes the PN code of the network station with the received packet and means for combining the phase-adjusted PN code with the received packet to spread spectrum decode the received packet, the phase adjusting means comprising means for searching for phase values synchronizing the PN code of the network station with the packet;
the base station being adapted to direct sequence spread spectrum encode each polling packet transmitted by the base station with the PN code of the base station phase-shifted according to a predetermined phase value;
each polled station being adapted to direct sequence spread spectrum encode each response packet of the polled station with the PN code of the polled station set at a phase value which synchronized the PN code of the polled station with the corresponding polling packet received by the station;
the searching means of the base station being adapted to search for phase values synchronizing the PN code of the base station with response packets generated by the polled stations, the searching means of the base station comprising means for:
a. setting upper and lower bounds for a restricted set of phase values corresponding to the predetermined phase value of the base station used to encode the polling packet corresponding to the response packet;
b. selecting different phase values for the PN code of the base station from the restricted set;
c. producing phase-shifted PN codes corresponding to the PN code of the base station shifted in phase according to each of the selected phase values;
d. combining the phase-shifted PN codes of the base station with the response packet to produce signals each corresponding to a different selected phase value;
e. detecting from the signals a phase value which synchronizes the PN code of the base station with the response packet.

10 more elements

Dependencies are inferred from the claim text.