Number of streams indication for WLAN

A method for generating a preamble of a data unit for transmission via a communication channel, the method comprising:nincluding a first indication of a first number of spatial or space-time streams in a first sub-field of a first field of the preamble, wherein the first number of spatial or space-time streams corresponds to transmission of the data unit to a first receiver;including one or more training sequences in a second field of the preamble;including in a second sub-field of the first field an indication of whether space-time block coding is to be used in transmitting the data unit via the communication channel;when the data unit corresponds to only one receiver,nincluding in a third sub-field of the first field an indication that the data unit corresponds to only one receiver, andincluding in a fourth sub-field of the first field of the preamble an indicator of the one receiver so that other receivers can determine that the data unit is not addressed to the other receivers;when the data unit corresponds to a group of multiple receivers,nincluding in the third sub-field an indication that the data unit corresponds to multiple receivers, andincluding in the fourth sub-field of the first field of the preamble a second indication of a second number of spatial or space-time streams, wherein the second number of spatial or space-time streams corresponds to transmission of the data unit to the second receiver; andformatting the preamble such that the first field of the preamble will be transmitted prior to the second field of the preamble being transmitted.

An apparatus, comprising:na physical layer (PHY) unit configured to:ngenerate a preamble of a data unit for transmission via a communication channel, wherein,nthe preamble includes a first field having in a first sub-field first indication of a first number of spatial or space-time streams corresponding to transmission of the data unit to a first receiver,the preamble includes a second field having one or more training sequences,the preamble includes a third field second sub-field of the first field having an indication of whether space-time block coding is to be used in transmitting the data unit via the communication channel,when the data unit corresponds to only one receiver,nthe preamble includes a third sub-field of the first field an indication that the data unit corresponds to only one receiver, anda fourth sub-field of the first field of the preamble includes an indicator of the one receiver so that other receivers can determine that the data unit is not addressed to the other receivers;when the data unit corresponds to a group of multiple receivers,nthe third sub-field of the first field includes an indication that the data unit corresponds to multiple receivers, andthe fourth sub-field of the first field of the preamble includes at least a second indication of a second number of spatial or space-time streams, wherein the second number of spatial or space-time streams corresponds to transmission of the data unit to the second receiver; andcause the first field of the preamble to be transmitted prior to the second field of the preamble being transmitted.

A method for processing a preamble of a data unit received via a communication channel using a first receiver, the method comprising:nreceiving a first field of the preamble, whereinna first sub-field of the first field includes a first indication of a first number of spatial or space-time streams of the data unit,a second sub-field of the first field includes an indication of whether the data unit is encoded using space-time block coding,a third sub-field of the first field includes an indication of whether (i) that the data unit corresponds to only one receiver, or (ii) the data unit corresponds to a group of multiple receivers;analyzing the third sub-field of the first field to determine whether (i) the data unit corresponds to only one receiver, or (ii) the data unit corresponds to the group of multiple receivers;when it is determined that the data unit corresponds to only one receiver, analyzing a fourth sub-field of the first field to determine whether a receiver indicator in the fourth sub-field of the first field corresponds to the first receiver;when it is determined that the data unit corresponds to the group of multiple receivers, analyzing the fourth sub-field of the first field to determine a second indication of a second number of spatial or space-time streams of the data unit;receiving one or more training sequences in a second field of the preamble after receiving the first field of the preamble; andutilizing one or more training sequences in the second field of the preamble to generate an estimate of at least a portion of the communication channel.

An apparatus for processing a preamble of a data unit received via a communication channel, the apparatus comprising:na physical layer (PHY) unit configured to:nreceive a first field of the preamble, wherein receiving the first field includesnreceiving a first sub-field of the first field, wherein the first sub-field includes a first indication of a first number of spatial or space-time streams of the data unit,receiving a second sub-field of the first field that includes an indication of whether the data unit is encoded using space-time block coding, andreceiving a third sub-field of the first field that includes an indication of whether (i) that the data unit corresponds to only one receiver, or (ii) the data unit corresponds to a group of multiple receivers;analyze the third sub-field of the first field to determine whether (i) the data unit corresponds to only one receiver, or (ii) the data unit corresponds to the group of multiple receivers;when it is determined that the data unit corresponds to only one receiver, analyze a fourth sub-field of the first field to determine whether a receiver indicator in the fourth sub-field of the first field corresponds to the first receiver;when it is determined that the data unit corresponds to the group of multiple receivers, analyze the fourth sub-field of the first field to determine a second indication of a second number of spatial or space-time streams of the data unit;receive one or more training sequences in a second field of the preamble after receiving the first field of the preamble; andutilize one or more training sequences in the second field of the preamble to generate an estimate of at least a portion of the communication channel.