The present invention relates to apparatuses and processes designed for use with a form of data transmission using packets. More particularly, the present invention relates to techniques for increasing efficiency in wireless LANs, satellite, broadcast and even wire transmissions by providing a more efficient grouping of the data packets so that the amount of data transmitted relative to the protocol requirements of the packets is increased.
For example, current wireless LANs, such as those operating under access protocols such as IEEE 802.11, have several different options for modulation and coding. The selection of these options is normally determined by the maximum data rate given the pack error rate is smaller than a given threshold.
However, since the selection criterion does not differentiate between the “service” by the upper layers, there are some traffic patterns that can dramatically reduce the efficiency of throughput. For example, today's 802.11 a/g protocol, though having a 54 Mbps data rate at the physical layer, has no more than 23 Mbps average throughput measured at the MAC-SAP (Service Access Point), which is the top gate of the MAC (Medium Access Control).
One of the reasons that the MAC is so inefficient is because according to statistics almost 75% of the packets are less than 128 bytes in length. Since the overhead length of a particular packet is fixed, the efficiency is low when packet length is short. Thus, there is a need to increase the efficiency of the MAC layer.
There is also a need to improve the current Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) multiple access scheme. One of the problems with 802.11 using CSMA/CA is that special packets (Request to Send, Acknowledge, Clear to Send) are used to alert every node on the wireless network that a transmitting node has data that it wants to send (as well as being ready to send), by broadcasting these packets throughout the network that are sent at the lowest radio speed, meaning that there is another problem with small packets in that the radio preamble is relatively large compared to the amount of data transmitted.
In addition, the PHY layer, which is tailored for a wireless LAN environment, may require an array of services that permit data transmission at a rate of near peak throughput of the packets, which is difficult with the inefficient transmission of short packets.
However, even with CSMA/CA there are problems with hidden transmitters (which occurs when one of the wireless nodes cannot hear at least one of the other wireless nodes) that cause detrimental interference by broadcasting at the same/overlapping times because they could not hear each other's broadcast of special packets.
Thus, what is needed is a way to increase the efficiency of packets so that they will be able to carry more data, thus spending relatively less time in sending all the portions of the packet that are required even with a minimal amount of data being transmitted in the short packets.
Accordingly, a new standard has been developed using a TDD/TDMA scheme for the next generation 802.11n (which is far more efficient than CSMA/CA). However, there exists a need to make the new standard TDD/TDMA backward-compatible in order to permit both access schemes to co-exist in the same frequency band so that older 802.11 legacy devices can still operate even though there has been a change in protocols for the newer devices.
The presently claimed invention provides a method, a system and an apparatus for providing a packet able to use/provide multiple services in TDMA and TDD with one of the services dedicated to short packet service, and is backwardly compatible with CSMA/CA. The presently claimed invention also improves the efficiency of the MAC layer and permits an array of services that allow data transmission at near peak rate throughput of the packets.
In addition, an array of services in the physical layer that are tailored for a wireless LAN environment are provided so as to maximize the throughput. For example, multiple concurrent services are enabled for scenarios like transmitting video contents and remote control information simultaneously.
It is to be understood by persons of ordinary skill in the art that the following descriptions are provided for purposes of illustration and not for limitation. An artisan understands that there are many variations that lie within the spirit of the invention and the scope of the appended claims. Unnecessary detail of known functions and operations may be omitted from the current description so as not to obscure the finer points of the present invention.
In this particular example (purely for purposes of illustration) client 1 device 120 may be an 802.11 legacy device 120 operating under CSMA/CA via AP 116. The contention issues regarding the legacy devices are handled via the dynamic contention packet 231 shown in
Thus, the legacy devices that were built for CSMA/CA can continue to communicate using CSMA/CA in their time slots. However, newer devices can communicate using the Superframe according to the present invention.
All client devices in general have to communicate with AP in order to connect to the network unless they use peer-to-peer service 232, and that includes new client devices that may operate using the superframe according to the present invention.
According to the invention, the superframe assigns different “times” to different devices to avoid collision for the forward link. For the reverse link, they sign up or contend in the second frame. The legacy devices still use DIFS, SIFS, etc., to facilitate communication, if, for example, the superframe were used to communicate to devices under 802.11.
In order to facilitate an understanding of the invention, a brief overview of Orthogonal Frequency Division Modulation is provided. Orthogonal Frequency Division Modulation (OFDM) is a technique that combines multiple low data rate carriers into a high data rate transmission that is a composite of the low data rate carriers. OFDM permits the placement of modulated carriers as close as possible, so as to not waste any of the bandwidth.
According to an aspect of the invention, the OFDM symbol period is about 4 us. Short symbol periods need to be used if it is desired to transmit at high data rates. A symbol period can be defined as being an inverse of the baseband data rate (T=1/R). The symbol period must be selected with care, because while it is desirable to have short symbol periods to transmit at high data rates, conversely, a shorter symbol period increases the likelihood for Inter-Symbol Interference (ISI). ISI happens when, for example a delayed version of sample “x” arrives not at its own processing period, but during a portion of the processing period of a subsequent sample (X+1).
In theory, the carrier of the next predetermined bandwidth would be adjacent to the current carrier so there would be no wasted spectrum. However, there is a likelihood that a drift in frequency may cause collisions. To prevent this problem from occurring, a guard band must be placed between each of the carrier bandwidths. The guard band is essentially wasted space, where a filter is used in the guard band to attenuate the signal of an adjacent carrier.
In the present invention, a Guard Time (GT) Interval 210 us is used, and is placed near the beginning of the superframe to ensure that there is no overlap from the previous transmission. The purpose of the GT is to prevent Inter-Carrier Interference (ICI). In this aspect of the invention, a guard time of 6us is provided, although it is possible that such a GT could be increased or decreased.
In addition, with regards to optimum times, the OFDM symbol 205 is about 4 us, and one slot is equal to 16 OFDM symbols, or 16 times×4 us or about 64 us in length. A slot, which is equal to 16 OFDM symbols=64 us. One frame is equal to (32 slots+GT)=512 symbols=2.24 ms. The superframe is thus about equal to 35.84 ms (16 frames+GT) in duration.
As shown in
It should be noted that each of the frames 3 to 16 can be assigned to one of the services from 225 to 232, which would result in a configuration that is different from what is shown in
It should be noted that the Dynamic Contention Service is mainly for legacy devices that operated under one of the earlier 802.11 protocols, and that the above list of items for payload frames do not necessarily correspond to a particular frame number, and might be more than one of the 3rd to the 16th frames.
In addition, with regard to the Dynamic Contention Service 231, it can vary from the 3rd to the 15th packet, and the end of the Contention Period is always 16. For example, while each frame may be assigned as one of the eight services 225 to 232, Dynamic Contention Service 231 could be assigned to several frames in a row but still has to be part of frames 3-16 (e.g., cannot use 1 or 2).
At step 310, it can be determined by the transmission/controller 113, 114, 115, 116 whether a particular device of thee or more wireless devices 120, 125, 130 to receive a wireless communication is a legacy device operating under Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol. Such a determination provides a portion of the backwards compatibility of the claimed invention.
At step 320 if the determination in step 310 is that there is a legacy device that operates under CSMA/CA protocol, the legacy device will receive transmission in a conventional fashion, and the transmission controller transmits a superframe that includes an enabled Dynamic Contention Packet service 232 that provides CSMA/CA protocols for backward compatibility;
At step 330, if the determination in step 320 is that said particular device of said one or more wireless devices 120, 125, 130 is not a legacy device operating under CSMA/CA, then the transmission controller transmits a superframe under TDD/TDMA.
At step 340, it is determined whether there is another wireless device requiring service. If so, the method repeats step 310 to determine whether another wireless device is a legacy device.
The superframe transmitted in both steps 320 and 330 comprises at least 16 packets, and one version of which is shown in
Various modifications to the above invention can be made by persons of ordinary skill in the art that do not depart from the spirit of the invention, or the scope of the appended claims. For example, the layout of the packets in the superframe shown in
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2005/052034 | 6/21/2005 | WO | 00 | 11/7/2007 |
Number | Date | Country | |
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60582592 | Jun 2004 | US |