The present invention relates generally to data communication, and more particularly, to data communication in wireless local area network (WLAN) environment.
The IEEE 802.11n standard provides for data communication, and more particularly, to data communication in WLAN environments. In IEEE 802.11n development process, a Multi-MCS-Multi-Receiver Aggregation (MMRA) mechanism has been proposed to increase the wireless LAN (WLAN) efficiency.
Implementing Multi-MCS-Multi-Receiver Aggregation (MMRA) requires a modification in the physical layer (PHY) aggregation. Compared to MRA, the MMRA technique can aggregate multiple packets with different transmission rates (MCS). MRA always uses the same MCS to transmit the aggregated packet to multiple receivers.
In one embodiment the present invention provides a method of communicating data over a wireless local area network according to an IEEE 802.11n proposal for Multi-MCS-Multi-Receiver Aggregation (MMRA), the improvement comprising providing a modified PPDU format with MMRA signaling wherein the HT-SIG format is preserved.
Instead of increasing the length of HT-SIG, a modified PPDU format with MMRA signaling is provided where the HT-SIG-MMRA is placed at the end of HT-LTF. In this manner, the original HT-SIG format described in S. A. Mujtaba, “TGn Sync Proposal Technical Specification,” a contribution to IEEE.802.11, 11-04-889r1, November 2004 (incorporated herein by reference) is preserved, while accommodating the variable length of HT-SIG-MMRA.
Further, in a modified HT-SIG structure according to an embodiment of the present invention, the Length and MCS of the HT-SIG-MMRA signaling part is placed in the LENGTH field and MCS field of HT-SIG1 (4 us), respectively, without changing the length of existing HT-SIG (8 us).
Further, two bits in HT-SIG2 (4 us) indicate aggregation: AGGREGATION and MRA bits.
These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures.
Initial 802.11 stations typically send frames in the order they are received. For throughput purposes, it is highly desirable to reorder frames so that they can coalesce into larger aggregated frames. Aggregation in TGnSync is a MAC-layer function that bundles several MAC frames into a single PLCP (Physical Layer Convergence Protocol) frame for transmission.
A single physical-layer frame contains several MAC layer frames. Several MAC frames are put into the same PLCP frame, with an appropriate delimiter between them. The delimiter has a small reserved field, a length field for the following MAC frame, a CRC to protect the delimiter, and a unique pattern to assist in recovering individual frames from the aggregate. MAC frames are put into the aggregate without modification, and contain the full header and MAC CRC. Even if one frame out of an aggregate is lost, it may be possible to successfully receive all the remaining frames.
However, the benefits of aggregation in TGnSync are not confined to pairs. Single-receiver aggregation is required; an optional extension allows aggregate frames to contain MAC frames for multiple receivers, in which case they are called Multiple Receiver Aggregate (MRA) frames. Inside the single rate transmitted aggregate frame, there are multiple Initiator Access Control frames. Each IAC specifies an offset to transmit the response to the aggregated frames, which will usually be a block acknowledgment response. To distinguish multiple receiver aggregate frames from single-receiver aggregate frames, multiple-receiver frames start with a control item called the Multiple Receiver Aggregate Descriptor (MRAD). The initiator's aggregate frame starts with the aggregate descriptor, and is followed by the aggregated frames for each destination. (802.11 Wireless Networks: The Definitive Guide, Second Edition”, by Matthew Gast, Second Edition, Ch. 15, April 2005 ISBN: 0-596-10052-3).
Implementing Multi-MCS-Multi-Receiver Aggregation (MMRA) requires a modification in the physical layer (PHY) aggregation. In IEEE 802.11n development process, a Multi-MCS-Multi-Receiver Aggregation (MMRA) mechanism has been proposed to increase the wireless LAN (WLAN) efficiency, as described in the TGnSync Technical Proposal in the attached Appendix. As noted,
According to one embodiment of the present invention shown by example in
After moving the HT-SIG-MMRA 202 to the location after the HT-LTF 204, the HT-SIG-MMRA 202 can be transmitted in higher data rate, compared with the lowest data rate transmission in conventional systems. The modified format 200 (
Further, referring to
Two bits in HT-SIG2 (4 us) indicate aggregation i.e. SMRA (Single MCS Multiple Receiver Aggregation), and MMRA, wherein: the AGGREGATION bit 306 indicates weather it is an aggregated packet and one more bit to indicate MMRA (e.g., the spare bit from ADV coding 308 can be used).
With AGGREGATION and MRA bits, the HT-SIG1 field can be interpreted by a receiver as:
AGGREGATION=0: Without aggregation, LENGTH and MCS fields in HT-SIG1 are interpreted as the length and MCS of the transmitting PSDU (PHY Service Data Unit), respectively.
AGGREGATION=1: With aggregation, MRA=0->SMRA, such that when MRA=0, the transmitting packet is a SMRA packet.
LENGTH and MCS fields 302, 304, in HT-SIG1 are interpreted by a receiver as the length and MCS of the transmitting PSDU, respectively. The LENGTH indicates the whole aggregated packet length. For example, two packet aggregates to a single PSDU, their length are l1 and l2 byte respectively. The LENGTH field in this case is l1+l2 bytes.
AGGREGATION=1: With aggregation, MRA=1->MMRA, such that when MRA=1, the transmitting packet is a MMRA packet.
LENGTH and MCS fields in HT-SIG1 are interpreted by a receiver as the Length and MCS of HT-SIG-MMRA, respectively. The Length and MCS for each aggregated packet are indicated in HT-SIG-MMRA. In one example, two packets are to be aggregated. One packet has length of 11 bytes and should be transmitted with MCS1. The other packet has length of l2 bytes and should be transmitted with MCS2. The value of l1, MCS1 and l2, MCS2 are placed into HT-SIG-MMRA 400 as shown in
The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.