HK1206165B - Systems and methods for high rate ofdm communications - Google Patents

Description

System and method for high-rate orthogonal frequency division multiplexing communications

Related application data

This application claims the benefit of and priority under 35 U.S.C. §119(e) to U.S. patent application Ser. No. 60/363,218, filed Mar. 8, 2002, entitled “High Rate OFDM Communication System and Method for Wireless LAN,” which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates generally to communication systems and, more particularly, to Orthogonal Frequency Division Multiplexing (OFDM) communication systems, methods, and protocols.

Background Art

The IEEE 802.11a and 802.11g standards for wireless local area networks, which are hereby incorporated by reference in their entirety and hereinafter referred to as 803.11a/g, specify wireless local area network communication systems in the 5 GHz and 2.4 GHz frequency bands. These standards specify the use of OFDM as the modulation method for communication. OFDM is a multi-carrier modulation scheme suitable for implementation in wireless communication channels. The 802.11a/g standards provide for data transmission rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps. The different data transmission rates are achieved by sending a different but constant number of bits on all carriers in the multi-carrier system and by operating at different coding rates. Table 1 below shows the coding rate and bits per subcarrier used for each data transmission rate for an exemplary 802.11a/g transceiver.

Table 1

To determine the appropriate data transmission rate to send, an 802.11a/g transmitter uses a trial-and-error method of transmitting at different data transmission rates, for example, starting with the highest or last successful transmission rate, and waiting for a positive acknowledgment from the receiver indicating that the data packet was successfully received. This simple positive acknowledgment method is used to optimize communications in conventional 802.11a-based wireless systems.

Summary of the Invention

The present invention illustrates a system and method that uses messages sent between a receiver and a transmitter to maximize communication data transmission rates. Specifically, according to an exemplary embodiment of the present invention, a multicarrier modulation system uses messages sent from a receiver to a transmitter to exchange optimized communication parameters. The transmitter then stores these communication parameters and, when transmitting to a particular receiver, utilizes the stored parameters to maximize the data transmission rate to that receiver. Similarly, when the receiver receives data packets from the particular transmitter, the receiver can utilize the stored communication parameters for reception.

Accordingly, aspects of the present invention relate to a multi-carrier modulation communication system.

Additional aspects of the present invention relate to a wired or wireless multi-carrier modulation communication system for transmitting messages between transceivers.

Additional aspects of the present invention relate to sending messages between multiple transceivers in an effort to optimize data communication rates.

A further aspect of the present invention relates to exchanging optimized communication parameters between multiple receivers in a multi-carrier modulation system.

Additional aspects of the present invention relate to exchanging communication parameters between a plurality of transceivers in a wired or wireless multi-carrier modulation communication network to adjust data transmission rates between the transceivers.

These and other features and advantages of the present invention are described in or are apparent from the following detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in detail with reference to the following drawings, in which:

FIG1 is a functional block diagram of an exemplary communication system according to the present invention;

FIG2 is a functional block diagram of first and second transceiver components according to the present invention;

FIG3 is a flow chart of an exemplary communication method according to the present invention;

FIG4 is an exemplary extended signal field according to the present invention;

FIG5 is a second exemplary communication system according to the present invention; and

FIG6 illustrates an exemplary transceiver according to a second exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The exemplary systems and methods of the present invention will be described below with respect to a multi-carrier modulation communication system. However, to make the present invention more clear, the following description omits well-known structures and devices, which can be generally illustrated in block diagram form or in other ways. For the purpose of explanation, many specific details are set forth to provide a thorough understanding of the present invention. However, it should be understood that, in addition to those specifically set forth in detail herein, the present invention can be practiced in various ways. For example, the systems and methods of the present invention can generally be applied to any type of communication system, including wired communication systems, wireless communication systems, such as wireless local area networks, power line communication systems, wired or wireless telephone line communication systems, or any combination thereof.

Furthermore, while the exemplary embodiments described herein illustrate various components of the communication system configuration, it should be understood that the various components of the system can be located on a remote portion of a distributed network, such as a telecommunications network and/or the Internet, or within a dedicated multi-carrier modulation system. Therefore, it should be understood that the components of the communication system can be combined into one or more devices or configured at specific nodes of a distributed network, such as a telecommunications network. As will be understood from the following description, for computational efficiency considerations, the components of the communication system can be located anywhere within the distributed network without affecting the operation of the system.

Furthermore, it should be understood that the various links connecting these units may be wired or wireless links, or any combination thereof, or any other known or later developed unit that is capable of providing and/or exchanging information into and out of these connected units. Additionally, the term module as used herein may refer to any known or later developed hardware, software, or combination of hardware and software that is capable of performing the functions associated with that unit.

Furthermore, although the present invention will be described with respect to a multi-carrier modulation system, the system and method of the present invention may be applied to any communication system or transmission protocol for transmitting information.

FIG1 illustrates an exemplary communication system 1. Communication system 1 includes one or more base stations 10 and an access point (AP) 20. This exemplary embodiment illustrates a wireless local area network (WLAN) in which multiple base stations 10 communicate with access point 20. In particular, in this exemplary WLAN, multiple base stations 10 share a common communication medium. One possible configuration includes an access point 20 for communication between base stations 10 (BSS). Access point 20 provides a local relay function between base stations 10 and, for example, to other wired and/or wireless networks (not shown). Therefore, when base station 1 communicates with base station 2, the communication (e.g., data packets) is sent from base station 1 to access point 20, and then from access point 20 to base station 2. For this reason, in most cases, base station 10 only sends and receives data packets to and from access point 20. Access point 20, on the other hand, must communicate with all base stations 10 in the network.

Another possible configuration does not rely on access points 20, but instead communicates directly between base stations 10 in the network (IBSS), as shown by the dashed lines in Figure 1. In this embodiment, communication occurs directly between base stations 10, with no relay functionality provided by access points 20.

According to an exemplary embodiment of the present invention, the wireless network relies on exchanging parameters between multiple transceivers, particularly from a receiver to a transmitter. These parameters are stored at the transmitter and used to subsequently transmit data packets to the receiver from which the parameters originated. Thus, the system and method of the present invention will function similarly regardless of whether the network is configured with access points 20 or not, as each base station, including the access point, if used, maintains a table containing the communication parameters.

Several different types of communication parameters can be sent from a receiver to a transmitter to optimize communications, such as increasing or decreasing the data transmission rate. In general, any parameter that can change performance can be included in the message. The following examples are some of the more common types of communication parameters that can be exchanged between a receiver and a transmitter.

Bit Allocation Table—In multicarrier modulation systems, a bit location table specifies the number of bits modulated on each carrier, also known as a subchannel, subcarrier, tone, or binary number. 802.11a/g transceivers use the same number of bits on all subchannels, which is the simplest bit location table. Because wireless communications experience multipath, the communication channel is not flat in frequency, meaning that different subcarriers will have different signal-to-noise ratios. Therefore, to achieve a constant bit error rate across all carriers, a bit location table is used so that carriers with higher signal-to-noise ratios modulate more bits than carriers with lower signal-to-noise ratios. This process is often referred to as "bit loading." Bit loading and bit location tables have been used in ADSL multicarrier communication systems for many years. For example, ITU standards G.992.1 and G.992.2, international ADSL standards that are incorporated herein by reference in their entirety, detail communications using bit loading and bit location tables. Bit loading also enables the use of constellation sizes higher than 64 QAM (6 bits), which is the maximum constellation size in standard 802.11a/g systems. If the channel supports it, modulation constellations with bit loading of 15 bits or more can be used, resulting in significant data rate improvements.

Coded Modulation Parameters - Systems using coded modulation techniques, such as trellis coded modulation and turbo coded modulation, achieve higher coding benefits than systems that do not combine modulation with forward error correction coding. However, coded modulation schemes do not encode all information bits; therefore, coded modulation must be combined with bit loading in multipath channels to realize the benefits of coding.

Variable Cyclic Prefix Length—A cyclic prefix is used in multicarrier systems to combat multipath. Generally, as long as the channel impulse response is less than the cyclic prefix length, there is no inter-symbol interference (ISI) or inter-channel interference (ICI) due to channel multipath. However, because the cyclic prefix is a redundant cyclic extension added to each communication symbol, it also results in a loss in data rate. The 802.11a/g standard uses a fixed cyclic prefix of 0.8 microseconds, which is 20% of the symbol length. Therefore, increasing the cyclic prefix results in a 20% decrease in data rate. This is a good compromise if the channel is approximately the same length as the cyclic prefix. However, if the channel is much shorter, for example, only 0.1 microseconds, it makes sense to reduce the cyclic prefix length to 0.1 microseconds, yielding a 19% improvement in data rate. Similarly, if the channel is much longer than 0.8 microseconds, the cyclic prefix should be extended to match the channel length, as the effective levels of ISI and ICI will likely significantly reduce the achievable data rate.

Variable pilot tone allocation - Standard 802.11a/g receivers use four fixed pilot tones that are spread across the transmit frequency band. This is necessary in 802.11a/g systems because the transmitter does not know which parts of the frequency band are deeply nulled due to multipath. According to an exemplary embodiment of the present invention, the receiver can communicate to the transmitter which carrier should be used for pilot tones. Since the receiver can determine which carriers have a high signal-to-noise ratio, the receiver can command the transmitter to place pilot tones on those high signal-to-noise ratio carriers. In fact, in many cases, a single high signal-to-noise ratio carrier is sufficient for all timing recovery needs, allowing the system to send data on the three carriers that the 802.11a/g system uses for pilot tones. This also provides an increase in data transmission rates when compared to standard 802.11a/g systems.

Alternatively, the communication system may not dedicate any carriers to pilot tones, i.e., all modulated carriers may be modulated with information bits. In this case, the carriers carrying the information bits can be used to implement a "decision-directed" timing recovery algorithm. For example, the carriers used for such a decision-directed algorithm will typically carry fewer bits than is practically permissible at a specified bit error rate, in order to provide a reference signal with a high signal-to-noise ratio.

Fine gain per carrier - Fine gain is used in ADSL standards such as G.992.1 to equalize the bit error rate across all carriers when bit loading is used. Fine gain is a small adjustment in the transmit power level that enables a subchannel to achieve the desired bit error rate for the system based on a specifically measured signal-to-noise ratio.

Throughout the following discussion, the exemplary embodiments of the present invention will focus on a bit configuration table as the primary optimized communication parameter that is exchanged between a plurality of base stations. This is done because the use of a bit configuration table is the most efficient way to achieve optimized communication and change the data transmission rate. However, it will be understood that other communication parameters, including but not limited to gain fine-tuning, trellis coded modulation, pilot tone position, variable cyclic prefix length, and the like, can still be exchanged between a plurality of base stations to achieve changes in the data transmission rate, with or without the bit configuration table.

In order to achieve a change in the data transmission rate, a message containing the communication parameters is sent from the receiver to the transmitter. These communication parameters can be communicated in a variety of ways. For example, the communication parameters can be sent to the transmitter as part of a positive acknowledgment data packet. In this case, after receiving the positive acknowledgment data packet, the transmitter will use the communication parameters contained in the positive acknowledgment data packet for the transmission of subsequent data packets. These communication parameters can also be sent as part of a management or data frame, a part of which is intended to exchange information between transceivers. For example, the communication parameters can be sent as part of an extended header field of any data packet sent between transceivers.

An exemplary embodiment of a protocol for exchanging communication parameters according to an exemplary embodiment of the present invention will be discussed below with reference to FIG1 and FIG2 . Specifically, FIG1 illustrates an exemplary network 1, such as a wireless network. Network 1 includes multiple base stations 10 and an access point 20 interconnected by multiple links. FIG2 illustrates an exemplary embodiment of components associated with first and second transceivers, such as base stations 10 or access points 20. Specifically, first transceiver 100 includes a message determination module 110, a communication parameter determination module 120, a data packet determination module 130, a transmitter 140, a receiver 150, a memory 160, and a controller 170, all of which are interconnected by a link (not shown). Second transceiver 200 includes a message determination module 210, a communication parameter determination module 220, a data packet determination module 230, a transmitter 240, a receiver 250, a memory 260, and a controller 270, all of which are interconnected by a link (not shown).

For ease of description, the exemplary method for a high-rate OFDM communication system will be described with respect to a first transceiver transmitting a data packet to a second transceiver. For example, the first transceiver may be base station 2, and the second transceiver may be access point 20. Alternatively, the first transceiver may be base station 2, the second transceiver may be base station 1, and so on. The relevant portion of the protocol begins with the first transceiver transmitting a data packet at a maximum possible data transmission rate, such as 54 Mbps for 802.11a/g, at the last successfully transmitted data transmission rate, or at a known data transmission rate.

Specifically, the data packet determination module 130 cooperates with the transmitter 140, the memory 160, and the controller 170 to coordinate transmission of this first data packet, i.e., before any optimized communication parameters are exchanged, and the data packet is sent using a standard fixed-size communication parameter setting, such as those specified in IEEE 802.11a/g, for example, a fixed six bits per tone on all carriers.

Next, if the receiver 250 of the second transceiver successfully receives the data packet from the first transceiver 100, the second transceiver 200, in cooperation with the data packet determination module 230, the transmitter 240, the memory 260, and the controller 270, again returns a positive acknowledgment data packet to the first transceiver. This positive acknowledgment data packet also includes the optimized communication parameters determined by the communication parameter determination module 220, to be used by the second transceiver 200 for subsequent reception of data packets from the first transceiver 100. For example, the positive acknowledgment data packet may include a bit configuration table having different bits for each subcarrier, e.g., based on channel characteristics measured by the second transceiver 200 and determined by the communication parameter determination module 220. Alternatively, or in addition, this acknowledgment data packet may also indicate any optimized transmission parameters as described above, such as one or more carriers that should be used as pilot tones as described above.

If the second transceiver 200 does not successfully receive the data packet from the first transceiver 100, the second transceiver 200 does not return a positive acknowledgment data packet to the first transceiver. In this case, the first transceiver 100 again cooperates with the data packet determination module 130, the transmitter 140, the memory 160 and the controller 170 to transmit the data packet at the next highest or another known standard data transmission rate.

If the first transceiver 100 receives a positive acknowledgment data packet, the first transceiver and the memory 160 cooperate to store the optimized communication parameters. The first transceiver 100 then uses the stored communication parameters for transmitting subsequent data packets to the second transceiver 200. The use of the optimized communication parameters is indicated in the header fields of the data packets sent from the first transceiver 100 to the second transceiver 200. For example, the message determination module 110 changes the header fields to indicate which optimized communication parameters are being used.

The receiver 250 of the second transceiver receives the data packet from the first transceiver 100 and determines which communication parameters are being used based on information in the data field of the data packet. This is accomplished, for example, by decoding the header field of the data packet, which indicates the optimized communication parameters being used. The data packet can then be demodulated and decoded based on the information contained in the data field in conjunction with the message determination/decoding module 210 using the optimized communication parameters sent from the second transceiver to the first transceiver in a previous positive acknowledgment data packet.

After the second transceiver 200 receives a data packet from the first transceiver 100 with a header field specifying which optimized communication parameters to use, the second transceiver 200 sends a positive acknowledgment back to the first transceiver 100. This positive acknowledgment may contain the same parameters as used for the last successfully received data packet, as an instruction to the second transceiver 200 to continue transmitting using the stored optimized communication parameters. Similarly, the positive acknowledgment may simply be a basic acknowledgment packet, as in a conventional 802.11a/g system, indicating that the data packet was successfully received at the second transceiver and that communication should continue using the same optimized communication parameters. If the optimized communication parameters accompany all positive acknowledgments during the extended communication session, this mechanism effectively tracks the optimized communication parameters.

Alternatively, the second transceiver 200 may send a new, second set of optimized communication parameters in the confirmation message. These new parameters may, for example, request a change in data transmission rate, such as a higher data transmission rate. In this case, after receiving the confirmation data packet, the first transceiver 100 may begin transmitting using the second set of optimized communication parameters.

In the event that the second transceiver 200 does not successfully receive the data packet transmitted by the first transceiver 100, wherein the data packet has a modified header field specifying which communication parameters are being used, the second transceiver 200 will not send a positive acknowledgment back to the first transceiver 100. In this case, the first transceiver 100 will determine that the optimized communication parameters are no longer valid and will restart the protocol by returning to the first step, where the first transceiver 100 will begin communicating at a known data transmission rate, such as the highest data transmission rate (e.g., 54 Mbps in an 802.11a/g system), using fixed/standard communication parameters.

After transmitting the data packet using the first set of optimized parameters, a positive acknowledgement is received at the first transceiver 100 from the second transceiver 200, and this positive acknowledgement contains the new,

In the case of the second set of optimized parameters, these new parameters should be used for subsequent data packet transmissions. However, after transmitting a data packet using the second set of optimized parameters, if the second transceiver 200 does not receive a positive acknowledgment data packet, then the second transceiver 200 reverts to the first step of the protocol, where the data packet is transmitted at a known, such as the next highest, data rate. However, in this case, the first transceiver can begin by transmitting using the first set of optimized communication parameters or by transmitting at a data rate using fixed/standard communication parameters (e.g., 54 Mbps in the 802.11a/g standard).

Alternatively, or in addition, the first transceiver 100 and the second transceiver 200 can periodically transmit "reference" or "training" data packets, which can be used by the receiver portion of the transceiver and the communication parameter determination module to determine optimized transmission parameters. For example, these training data packets can be data packets containing signals known to the transceiver. For example, the training data packets can be data packets carrying non-information that are sent during a period when no data is being transmitted between the base station and the network. Because these data packets are predetermined and known to the receiver before reception, the receiver can use them to accurately measure the effects of the channel, such as multipath distribution, signal-to-noise ratio of each carrier, etc. These training data packets can also be used to train a receiver equalizer, which is used to equalize, for example, the wireless channel and/or receiver filters and/or transmitter filters.

In conventional wireless local area network systems, each data packet includes a header field that indicates the data transmission rate used to transmit the data field of the data packet. This header field is sent using a fixed modulation/coding scheme, such as the 802.11a/g standard, and can therefore be demodulated by all base stations. According to an exemplary embodiment of the present invention, the header field also indicates whether optimized communication parameters are used to transmit the data field in the data packet. This can be achieved in a variety of ways. For example, the header field can include an indication of the data transmission rate as in 802.11a/g. Alternatively, the header field can include a bit field that indicates whether the optimized communication parameters will be used. This bit field can be a single bit, indicating whether the optimized communication parameters from the previous exchange are to be used or one of the standard fixed communication parameters. Alternatively, the bit field can be multiple bits indicating one of multiple optimized communication parameter sets.

In the example of a network with access point 20, each base station transmitter will store optimized communication parameters to be used when sending data packets to access point 20. These optimized parameters will be generated by the access point 20 receiver and sent to the base station as described above. Obviously, since each base station 10 is located in a different location and may be mobile, each base station transmitter may have different optimized parameters to use when sending data packets to access point 20. Access point 20 must also store these optimized parameters, which are then used by the access point 20 receiver when receiving data packets from different base stations 10. Access point 20 may have a different set of optimized parameters for each base station 10. Since access point 20 receives data packets from all base stations, it must be able to determine the parameters used for the data packet based on information in the packet header (i.e., the signal field). Access point 20 can use the packet header to determine whether the optimized parameters are used, but since access point 20 does not know which base station actually sent the data packet, access point 20 cannot determine the correct parameters based on the header alone.

Therefore, according to an exemplary embodiment of the present invention, the header also includes a bit field that indicates which base station sent the data packet. In this case, access point 20 will use this information to determine which set of parameters to use. Alternatively, access point 20 may use other means to determine which base station sent the data packet. For example, access point 20 may use the power of the received signal, a channel estimate based on frequency equalizer taps, a carrier offset value, etc.

In a network example such as a wireless local area network with access point 20, the access point transmitter will store optimized communication parameters to be used when sending data packets to a particular base station 10. These optimized communication parameters will be generated by the base station receiver and transmitted to access point 20 as described above. Obviously, since each base station is located in a different location, the access point 20 may have multiple different sets of optimized communication parameters to use when sending data packets to different base stations 10. Then, when receiving data packets from the access point 20, each base station 10 also stores the optimized communication parameters corresponding to that base station to be used by the base station receiver. Each base station 10 should also be able to determine the communication parameters used for the data field based on information in the packet header (i.e., the signal field). Therefore, each base station 10 uses the packet header to determine whether the optimized communication parameters have been used. Unlike the access point receiver, each base station receiver is intended to receive data packets only from access point 20, so the base station 10 may be able to determine the communication parameters based solely on the header.

Since all base stations will receive data packets from access point 20, each base station must also be able to determine the communication parameters used for the data field based on the preamble and packet header (i.e., the signal field). Obviously, if the data packet is not designed for a specific base station receiver, the receiver may use incorrectly optimized communication parameters to receive the data packet. This is not a problem in practice because the data packet was not designed for the receiver in the first place. However, since the protocol requires the transmitter to comply with communications already in progress, each base station must be able to determine different protocol counters based on the duration of the data packet. Even if the use of incorrect communication parameters does not allow the receiver to correctly decode the message, the header must provide a way to determine the duration of the data packet.

As described above, once the receiving transceiver determines the optimized transmission parameters, the receiving transceiver needs to send this information to the transmitting transceiver for subsequent communication between the two devices. In addition, as discussed above, the optimized transmission information can be sent as part of an acknowledgment data packet. Alternatively, or in addition, the optimized transmission parameters can be exchanged as part of a management frame or a rule information carrying frame on a regular basis or, for example, on a triggered basis. In both cases, the optimized transmission parameters can be sent as part of an extended packet header field (also known as a signal field) or as part of the data packet information field. In the case of an extended packet header field, the information is sent at a fixed rate and can be decoded by all systems in the network. For example, a bit in the packet header field can be used to indicate that a new set of optimized transmission parameters has been appended to the extended packet header field.

In the latter case, the information can be sent using optimized parameters for communication. Note that in this case, the optimized transmission parameters used to send the optimized transmission parameter information from the receiver to the transmitter are different. For example, assume that the receiver of the first transceiver 150 determines optimized transmission information for transmitting a data packet from the transmitter 240 of the second transceiver to the receiver 150 of the first transceiver. The transmitter 140 of the first transceiver sends a data packet to the receiver 250 of the second transceiver, where the data packet includes the optimized transmission parameters used for transmitting the data packet from the transmitter 240 of the second transceiver to the receiver 150 of the first transceiver. The data packet sent from the transmitter 140 of the first transceiver to the receiver 250 of the second transceiver can be sent using a standard fixed rate, as in a conventional 802.11a/g system, or it can be sent using optimized transmission parameters exchanged between the first transceiver 100 and the second transceiver 200. It is apparent that the optimized transmission parameters for transmission from the first transceiver 100 and the second transceiver 200 have previously been exchanged during the communication session.

FIG3 is a flow chart of a conventional exemplary method for exchanging communication parameters according to the present invention. Specifically, control begins at step S100 and continues to step S110. In step S110, a first transceiver (designated T1) determines and sends a data packet to a second transceiver (designated T2) at at least one of a known, highest, last successful, or variable rate. Next, in step S120, a determination is made as to whether the data packet was successfully received at the second transceiver. If the data packet was not successfully received, control jumps to step S130. Otherwise, control continues to step S140.

In step S130, the communication parameter specifying the data transmission rate is increased/decreased according to the situation. Then, control continues back to step S110.

In step S140, the second transceiver returns a positive acknowledgment to the first transceiver, which may or may not include the optimized communication parameters. If the positive acknowledgment includes the optimized communication parameters, the second transceiver stores the parameters. Next, in step S150, the first transceiver receives the acknowledgment. Then, in step S160, if the positive acknowledgment returned from the second transceiver includes the communication parameters, the first transceiver stores the optimized communication parameters. Control then continues to step S170.

In step S170, the first transceiver determines a header field. Then, in step S180, the first transceiver begins communication using the stored optimized communication parameters. Then, in step S190, a determination is made as to whether the second transceiver has received the data packet. If the data packet has been received, control continues to step S200. Otherwise, control jumps to step S130.

In step S200, the second transceiver decodes the header field and determines the communication parameters to be used. Next, in step S210, the second transceiver demodulates and decodes the data field using the stored optimized communication parameters. Then, in step S220, the second transceiver determines that an acknowledgment is returned to the first transceiver. Control then continues to step S230.

In step S230, the second transceiver sends the confirmation to the first transceiver. This message may or may not include the optimized communication parameters. Control then continues to step S240, where the control process ends.

The basic concepts discussed above can also be extended to legacy systems. In the following discussion, base stations that only implement the current 802.11a/g standard will be referred to as legacy base stations. Base stations that can provide high-speed data communication using optimized communication parameters using the methods of the present invention are referred to as extended rate (ER) base stations. The methods and protocols that enable exchange, transmission, and reception using these optimized communication parameters are referred to as extended rate systems and protocols. In this exemplary embodiment, an extended rate base station also supports the current 802.11a/g standard.

For example, FIG. 5 shows an exemplary communication system 500 that includes a plurality of extended rate base stations 510 , 520 , one or more conventional base stations 530 , and, for example, an access point 540 .

When operating in an environment with both legacy base stations 530 and extended rate base stations 510, 520, there are two primary interoperability requirements to ensure network stability. First, the legacy base station 530 must be able to receive the ER packet header (Signal field) and use the Signal field parameters to correctly determine the data packet duration, i.e., the time required for data packet transmission. This ensures that the legacy base station 530 correctly sets its Network Allocation Vector (NAV) and other related counters so that accurate operation of the contention algorithm for medium access is maintained.

Secondly, if the data packet is intended for that base station, the extended rate base station 510, 520 must be able to determine the transmission parameters, such as the bit allocation table, based on the extended rate packet header. Furthermore, extended rate base stations that are not intended to receive the data packet must also use the signal field parameters to correctly determine the data packet duration, i.e., the time required for packet transmission. This ensures that the extended rate base station correctly sets its network allocation vector and other related counters so that accurate operation of the contention algorithm used for medium access is maintained.

To ensure that both of the aforementioned requirements are met, FIG4 illustrates an exemplary modified packet header using an extended signal field. In this illustrative 802.11a example, the signal field is extended. The first portion of the extended signal field has the same structure as the standard 802.11a signal field header. The first symbol of the extended signal field is modulated according to the signal modulation and coding parameters specified in IEEE 802.11a for the standard signal field, namely, 6 Mbps BPSK with a code rate of 1/2. Therefore, a legacy base station can correctly receive the signal field bits from the first portion of the extended signal field.

In the next symbol, the second portion of the extended signal field contains the transmitter (TX) and receiver (RX) base station identifiers. These extended signal field bits are also modulated using the 802.11a 6 Mbps, code rate = 1/2 modulation method. In Figure 4, these extended signal field bits are sent in the second symbol of the extended signal field header, which corresponds to data symbol number one in standard 802.11a systems.

Since there are both traditional and extended rate base stations in the exemplary communication system 500 shown in Figure 5, an extended rate base station needs to be able to determine and identify when a received data packet contains an extended signal field header, which is contained in two code elements, in contrast to the standard 802.11a header, which is contained in only one code element. This can be achieved by setting a bit in the standard 802.11a signal field. This bit will be referred to as the ER enable bit. As an example, the bit reserved between the rate (RATE) field and the length (LENGTH) field in 802.11a can be used as the ER enable bit. For example, when this reserved bit (R) is set to 1, this indicates that an extended rate header is being used. When this reserved bit (R) is set to 0, this indicates that a standard 802.11a header is being used.

Referring again to FIG5 , two ER base stations 510 and 520, a legacy base station 530, and an extended rate access point 540 are shown. In FIG5 , the different links represent, for example, the communication paths of an extended rate data packet, where the ER enable bit (R) is marked in the reserved bit R position and the transmitter/receiver base station identifier (TX/RX STA ID) is present in the extended signal field.

The following discussion will focus on exemplary communications occurring between different base stations, with reference to Figures 5 and 6. In particular, Figure 6 illustrates exemplary components that may be present in the base station of Figure 5. Specifically, base station 600 includes a message determination module 610, a communication parameter determination module 620, a data packet determination module 630, an ER detection module 640, a base station ID decoder/encoder 650, a receiver 660, a transmitter 670, a memory 680, and a controller 690. Many of the components shown in base station 600 are similar to those found in first transceiver 100 and second transceiver 200. Therefore, the functionality of these components as they relate to this embodiment of the present invention will not be discussed further.

Communication path 1: Data packets are transmitted from access point 540 to an ER-enabled base station, such as ER base station 510 .

The access point 540 forwards a data packet to the ER base station 510. The ER base station 510 detects the ER enable bit with the cooperation of the ER detection module 640 and determines that the data packet is an ER data packet.

Next, base station ID decoder/encoder 650 decodes the RX STA ID bits and the extended header fields to determine whether the received data packet is intended for this specific base station. ER base station 510, in cooperation with base station ID decoder/encoder 650, also decodes the TX STA ID in the extended rate header and determines whether the data packet is from access point 540. Based on this information, receiving extended rate base station 510 uses the stored optimized communication parameters used when receiving the data packet from access point 540. Extended rate base station 510 uses these optimized parameters to correctly decode the remaining fields of the data packet, namely the data field. Naturally, the RX base station had already sent these optimized communication parameters to the access point earlier in the session.

Communication path 2: Another ER-enabled base station, such as base station 520 , occasionally receives data packets from access point 540 .

The base station 520 cooperates with the ER detection module 640 to detect the ER enable bit in the data packet sent from the access point 540 and determine that the data packet is an ER data packet, and cooperates with the STA ID decoder/encoder 650 to decode the RX STA ID bit in the extended header field and determine that the received data packet is not intended for this particular base station. Then, based on the "spoofed" rate and length information contained in the signal field, the base station 520 sets the network allocation vector and associated counters, as described below.

Since base station 520 determines that the received data packet is not intended for it, base station 520 does not even need to decode the data packet. An additional benefit of this approach is that when a data packet is received, the base station can detect very early whether it is the intended recipient of the data packet, and therefore, if not, the base station does not need to decode the remainder of the data packet. This can, for example, save power in the base station because the base station does not expend the processing power required to decode the remainder of the data packet, and thus, for example, the base station can enter a low-power mode.

Communication path 3: The legacy base station 530 occasionally receives data packets originating from the access point 540 .

Legacy base stations are generally unaware of the ER packet header. Therefore, with the exception of the ER enable bit, which the legacy base station 530 should ignore (because it is redundant), the legacy base station 530 will correctly decode the first portion of the ER data packet, which is contained in the first symbol of the header field and is identical to the standard 802.11a signal field.

Based on the "spoofed" rate/length information contained in the SIGNAL field, the legacy base station 530 sets the network allocation vector and associated counters, as discussed below, to allow correct legacy operation of the 802.11a medium occupancy algorithm. Using this spoofed rate and length information, the legacy base station 530 will incorrectly demodulate the data symbols because the base station is unaware of the optimized communication parameters until a CRC error eventually causes the data packet to be ignored.

Communication path 4: Data packets are transmitted from the ER-enabled base station 510 to the access point 540 .

Access point 540 detects the ER enable bit, determines that the received data packet is an ER data packet, and decodes the RX STA ID bit in the extended header field to determine whether the data packet is intended for it. Access point 540 also decodes the TX STA ID in the ER header and determines which base station sent the data packet. Based on this information, access point 540 uses the stored optimized communication parameters to use when receiving data packets from that particular transmitter base station. Access point 540 then uses the optimized parameters to correctly decode the remaining fields of the data packet, namely the data field. Of course, access point 540 had already sent the optimized communication parameters to the transmitter base station earlier in the communication session.

Communication path 5: Another ER-enabled base station 520 occasionally receives data packets originating from the ER base station 510.

The base station 510, with the cooperation of the ER detection module, detects the ER enable bit to determine that this is an ER data packet, and, with the cooperation of the STA ID decoder/encoder 650, decodes the RX ST ID bit in the extended header field to determine that the data packet is not intended for it. Then, as discussed below, based on the "spoofed" rate and length information contained in the SIGNAL field, the base station 510 sets the network allocation vector and associated counters. Since the base station 510 knows that the data packet is not intended for it, it does not even need to decode the data packet. An additional benefit of this approach is that, when this happens, the base station can detect early on that it is not the intended recipient of the data packet, and therefore does not need to decode the remainder of the data packet. This saves power at the base station, for example, because the base station does not expend processing power decoding the remainder of the data packet, and thus can, for example, enter a low-power mode.

Communication path 6: The legacy base station 530 occasionally receives data packets originating from the ER-enabled base station 510 .

This situation produces the same result as shown with respect to communication path 3 .

"Spoofing" the rate and length fields.

When a legacy base station receives an ER data packet, such as in communication paths 3 and 6, it must be able to determine the data packet's duration—that is, the time required for packet transmission—based on the standard 802.11 header contained in the first symbol of the ER packet's header, which each base station can correctly decode. Therefore, for the legacy base station, bits R1-R4 have no meaning for an ER-enabled RX STA and must be set to a reasonable pattern used in the 802.11a standard, as shown in Table 1. Additionally, the Length field must be populated along with the Rate field in such a way that the legacy RX STA calculates the time required for data packet transmission based on the "spoofed" rate and length parameters that will coincide with those required by an ER RX STA using optimized communication parameters. This ensures that the legacy base station correctly sets its Network Allocation Vector and other related counters, thereby maintaining accurate operation of the contention algorithm used for medium access.

When a data packet is not intended for reception by an ER-enabled RX STA, such as in cases 2 and 5, the ER-enabled RX STA will also use the spoofed rate and length information shown in the SIGNAL field. Once the ER-enabled RX STA confirms that the reserved bit (R) is on, it examines the extended SIGNAL symbol and, based on the RX STA ID, determines that the data packet is not intended for it. Based on the "spoofed" rate and length information in the SIGNAL field, the RX STA sets a counter using a virtual carrier sensing algorithm in exactly the same manner as a conventional base station and can then enter power saving mode.

As an example, the ER data transmission rate is 108 Mbps, which is twice the maximum data transmission rate of a conventional 802.11a system (54 Mbps). This can be achieved, for example, through bit loading and the use of trellis-coded modulation. A system transmitting at 108 Mbps would have 432 data bits per symbol. Therefore, for example, sending an 864-byte data packet would require 864*8/432 = 16 symbols. Furthermore, compared to a standard 802.11a system, the ER protocol requires an additional symbol in the ER header, which contains the TX and RX base station IDs. Therefore, sending an 864-byte data packet at 108 Mbps requires 16+1 = 17 symbols. To allow a legacy 802.11a base station to correctly determine the network allocation vector, the rate and length fields of the ER header need to be set so that the legacy base station will also determine that 17 symbols are required to transmit the data packet. Therefore, for example, the rate and length fields can be set to rate = 54 Mbps and length = 459 bytes. In this case, since 54 Mbps results in 216 data bits per symbol, the legacy base station will determine that the data packet duration is 459*8/216=17 symbols and correctly set the network allocation vector. Obviously, other rate and length combinations from the 802.11a standard can be used to enable the legacy base station to correctly set the network allocation vector. For example, rate = 6 Mbps and length = 51 bytes will also result in a data packet with a data field that is 17 symbols long.

In the example described above, the extended header field contains only the RX and TX STA IDs. This implies that there is only one set of optimized parameters for each TX/RX communication. In another embodiment, the extended header field also (or alternatively) contains an indication of which of multiple optimized communication parameter sets will be used for transmitting and receiving data packets. These parameter sets are sent from the receiver base station to the transmitter base station and are stored in each.

The communication systems described above can be implemented on wired or wireless communication devices, such as modems, multi-carrier modems, DSL modems, ADSL modems, XDSL modems, VDSL modems, multi-carrier transceivers, wired or wireless wide area network/local area network systems, etc., or on separate programmed general-purpose computers with communication devices. In addition, the systems, methods, and protocols of the present invention can be implemented on special-purpose computers, programmed microprocessors or microcontrollers and external integrated circuit units, ASICs or other integrated circuits, digital signal processors, hard-wired electronic or logic circuits, such as discrete component circuits, programmable logic devices (such as PLDs, PLAs, FPGAs, PALs), modems, transmitters/receivers, etc. In general, any device capable of executing a state machine can be used to implement the various communication methods according to the present invention, which state machine can then execute the flowcharts shown herein.

In addition, the disclosed method can be easily implemented in software using an object or object-oriented software development environment, which provides portable source code that can be used on various computer or workstation platforms. In addition, the disclosed communication system can be implemented in part or completely in hardware using standard logic circuits or VLSI designs. Whether software or hardware is used to implement the system according to the present invention depends on the speed and/or efficiency requirements of the system, as well as the specific functions and specific software or hardware systems or microprocessors or microcomputer systems used. However, the communication systems, methods and protocols shown here can be easily implemented by those skilled in the art from the functional description provided here, using any known or later developed system or structure, equipment and/or software, and with the help of the basic knowledge of computer and telecommunication fields routine, with hardware and/or software.

Furthermore, the disclosed methods may be readily implemented as software executed on a programmed general purpose computer, a special purpose computer, a microprocessor, etc. In this case, the system and method of the present invention may be implemented as a program embedded on a personal computer, such as a CGI script, as a resource resident on a server or graphics workstation, as a routine embedded in a dedicated communication system, etc. The communication system may also be implemented by physically incorporating the system and method into a software and/or hardware system, such as the hardware and software system of a communication transceiver.

It is therefore apparent that a system and method for exchanging communication parameters according to the present invention has been provided. While the present invention has been described in conjunction with a number of embodiments, it is apparent that numerous alternatives, modifications, and variations will be apparent to those skilled in the art. It is therefore intended that all such alternatives, modifications, equivalents, and variations within the spirit and scope of the present invention be encompassed by the appended claims.

Claims (52)

1. A method for transmitting data packets, the method comprising: Transmit a data packet having a signal field including a spoofing rate and a length value contained in a first symbol of the signal field, wherein a legacy station correctly decodes the spoofing rate and length value in the first symbol of the signal field, and wherein a legacy station incorrectly demodulates the data symbol of the data packet using the spoofing rate and length value, wherein the data packet originates from an extended rate access point or an extended rate enabled station. 2. The method of claim 1, wherein the signal field and the data symbols of the data group are modulated using different parameters. 3. The method of claim 1, wherein the length value represents the number of bytes. 4. The method of claim 1, wherein the spoofing rate is expressed in bits per second (bit rate). 5. The method of claim 1, wherein the spoofing rate and length values are used to determine the time required for data packet transmission. 6. The method of claim 1, wherein the spoofing rate and length values are used to set the network allocation vector. 7. The method of claim 1, wherein the conventional station is an 802.11g station. 8. The method of claim 1, wherein the spoofing rate and length values are used to determine the duration required for the transmission of data packets. 9. The method of claim 1, wherein the signal field is extended to represent at least one of a bit allocation table, lattice coding, turbo coding, variable cyclic prefix length, and variable pilot tone allocation. 10. A method for receiving data packets, the method comprising: A data packet is received having a signal field including a spoofing rate and a length value contained in a first symbol of the signal field, wherein a legacy station correctly decodes the spoofing rate and length value in the first symbol of the signal field, and wherein a legacy station incorrectly demodulates the data symbols of the data packet using the spoofing rate and length value, wherein the data packet originates from an extended rate access point or an extended rate enabled station. 11. The method of claim 10, wherein the signal field and the data symbols of the data group are modulated using different parameters. 12. The method of claim 10, wherein the length value represents the number of bytes. 13. The method of claim 10, wherein the spoofing rate is expressed in bits per second (bit rate). 14. The method of claim 10, wherein the spoofing rate and length values are used to determine the time required for data packet transmission. 15. The method of claim 10, wherein the spoofing rate and length values are used to set the network allocation vector. 16. The method of claim 10, wherein the conventional station is an 802.11g station. 17. The method of claim 10, wherein the spoofing rate and length values are used to determine the duration required for the transmission of data packets. 18. The method of claim 10, wherein the signal field is extended to represent at least one of a bit allocation table, a lattice coding technique, a turbo coding technique, a variable cyclic prefix length, and a variable pilot tone allocation. 19. An extended rate-enabled station capable of transmitting data packets having a signal field containing spoofing rate and length values, the spoofing rate and length values being contained in a first symbol of the signal field, wherein a conventional station correctly decodes the spoofing rate and length values in the first symbol of the signal field, and wherein a conventional station incorrectly demodulates the data symbols of the data packet using the spoofing rate and length values. 20. The extended rate enable station of claim 19, wherein the signal field and the data symbols of the data packet are modulated using different parameters. 21. The extended rate enable station as claimed in claim 19, wherein the length value represents the number of bytes. 22. The extended rate enabler as claimed in claim 19, wherein the spoofing rate is expressed in bits per second (bit rate). 23. The extended rate-enabled station of claim 19, wherein the spoofing rate and length values are used to determine the time required for data packet transmission. 24. The extended rate enable station as claimed in claim 19, wherein the spoofing rate and length values are used to set the network allocation vector. 25. The extended rate-enabled station of claim 19, wherein the conventional station is an 802.11g station. 26. The extended rate enabling station of claim 19, wherein the spoofing rate and length values are used to determine the duration required for the transmission of data packets. 27. The extended rate enable station of claim 19, wherein the signal field is extended to represent at least one of a bit allocation table, lattice coding, turbo coding, variable cyclic prefix length, and variable pilot tone allocation. 28. A station capable of receiving data packets having a signal field containing spoofing rate and length values, the spoofing rate and length values being contained in a first symbol of the signal field, wherein a conventional station correctly decodes the spoofing rate and length values in the first symbol of the signal field, and wherein a conventional station incorrectly demodulates the data symbols of the data packet using the spoofing rate and length values, wherein the data packet originates from an extended rate access point or an extended rate enabled station. 29. The station of claim 28, wherein the signal field and the data symbols of the data packet are modulated using different parameters. 30. The station of claim 28, wherein the length value represents the number of bytes. 31. The station of claim 28, wherein the spoofing rate is expressed in bits per second (bit rate). 32. The station of claim 28, wherein the spoofing rate and length values are used to determine the duration required for the transmission of data packets. 33. The station of claim 28, wherein the spoofing rate and length values are used to set the network allocation vector. 34. The station as claimed in claim 28, wherein the conventional station is an 802.11g station. 35. The station of claim 28, wherein the signal field is extended to represent at least one of a bit allocation table, lattice coding, turbo coding, variable cyclic prefix length, and variable pilot tone allocation. 36. An apparatus for transmitting data packets, the apparatus comprising: A means for transmitting a data packet having a signal field including a spoofing rate and a length value contained in a first symbol of the signal field, wherein a legacy station correctly decodes the spoofing rate and length value in the first symbol of the signal field, and wherein a legacy station incorrectly demodulates the data symbol of the data packet using the spoofing rate and length value, wherein the data packet originates from an extended rate access point or an extended rate enabled station. 37. The apparatus of claim 36, wherein the signal field and the data symbols of the data packet are modulated using different parameters. 38. The apparatus of claim 36, wherein the length value represents the number of bytes. 39. The apparatus of claim 36, wherein the spoofing rate is expressed in bits per second as a bit rate. 40. The apparatus of claim 36, wherein the spoofing rate and length values are used to determine the duration required for the transmission of data packets. 41. The apparatus of claim 36, wherein the spoofing rate and length values are used to set the network allocation vector. 42. The apparatus of claim 36, wherein the conventional station is an 802.11g station. 43. The apparatus of claim 36, wherein the signal field is extended to represent at least one of a bit allocation table, a lattice coding technique, a turbo coding technique, a variable cyclic prefix length, and a variable pilot tone allocation. 44. An apparatus for receiving data packets, the apparatus comprising: A means for receiving data packets having a signal field containing spoofing rate and length values, the spoofing rate and length values being contained in a first symbol of the signal field, wherein a legacy station correctly decodes the spoofing rate and length values in the first symbol of the signal field, and wherein a legacy station incorrectly demodulates the data symbols of the data packet using the spoofing rate and length values, wherein the data packet originates from an extended rate access point or an extended rate enabled station. 45. The apparatus of claim 44, wherein the signal field and the data symbols of the data packet are modulated using different parameters. 46. The apparatus of claim 44, wherein the length value represents the number of bytes. 47. The apparatus of claim 44, wherein the spoofing rate is expressed in bits per second as a bit rate. 48. The apparatus of claim 44, wherein the spoofing rate and length values are used to determine the duration required for the transmission of data packets. 49. The apparatus of claim 44, wherein the spoofing rate and length values are used to set the network allocation vector. 50. The apparatus of claim 44, wherein the conventional station is an 802.11g station. 51. The apparatus of claim 44, wherein the signal field is extended to represent at least one of a bit allocation table, a lattice coding technique, a turbo coding technique, a variable cyclic prefix length, and a variable pilot tone allocation. 52. A machine-readable medium having instructions stored thereon, which, when executed, cause the machine to perform the method as claimed in any one of claims 1-18.