HK1161450A - Method and apparatus for performing constellation scrambling in a multimedia home network - Google Patents

Description

Method and apparatus for performing constellation scrambling in a multimedia home network

Cross Reference to Related Applications

The priority of U.S. provisional application serial No. 61/105,942 filed on 16/10/2008, the priority of U.S. provisional application serial No. 61/144,061 filed on 12/1/2009, and the priority of U.S. non-provisional application serial No. 12/580,227 filed on 15/10/2009, are claimed, each of which is incorporated herein by reference in its entirety.

Technical Field

The disclosed methods and apparatus relate generally to communication networks, and more particularly some embodiments relate to constellation scrambling in orthogonal frequency division multiple access networks.

Background

With many continuing advances in communication and data transmission technologies, more and more devices are being introduced in the consumer and business areas of advanced high bandwidth communication capabilities. In addition, advances in processing power and low power consumption technologies have widely led to a proliferation of communication capabilities of various products.

For example, communication networks are becoming commonplace in many home and office environments today. Such networks allow many independent devices to share data and other information previously to enhance productivity or simply to improve convenience to users. In this context, there is an increasing demand for the ability to connect content devices (e.g., televisions, DVD players and recorders, digital cameras, speakers, video cameras, etc.), computing devices, I/O devices, appliances, and modems.

Home entertainment networks are typically provided in one of two topologies. The first is an access topology, which may best resemble a tree structure, where the base node communicates with nodes in its legs, but the leg nodes typically do not communicate directly with other legs. The second is a mesh topology, where any node can communicate directly with any other node in the network. An access topology typically exists in a cell or office setting where a master node at the "source" is used to distribute data to multiple downstream nodes (e.g., to many cells in a cell building) and the downstream nodes (e.g., cells) do not have to share content with each other. On the other hand, a mesh topology may more typically exist in a home environment, although there may be a common source of broadband data (the main cable feeds in the house), but the homeowner may wish to share content from devices in one room with other devices in other rooms in his home.

To address the ever-increasing demand in the digital home network market, the industry-leading association of enterprises formed the multimedia over coax alliance (MoCA)^TM). MoCA has provided a technical standard (referred to as "MoCA") defining protocols for distributing digital entertainment over available bandwidth on coaxial cable previously installed in homes for cable or satellite TV services. The initial MoCA standard was approved in 2006, month 2, and routers, MoCA set-top boxes, and MoCA adapters with built-in MoCA capabilities (i.e., compliant with the MoCA standard) soon appeared later. Thus, the MoCA standard defines a mesh topology.

The architecture of these and other networks, and the practical communication channels in general, have long struggled to overcome the challenges of various devices managing multiple communications over a limited channel. Accordingly, network architectures have proposed various schemes to arbitrate disputes or otherwise allocate bandwidth among various communication devices or clients on the network. Schemes used in known network architectures such as token ring, ethernet or other configurations have been developed to allow sharing of available bandwidth.

Disclosure of Invention

In accordance with various embodiments of the disclosed method and apparatus, a system and method are provided that allow multiple transmitting network devices to transmit to a receiving network device in an Orthogonal Frequency Division Multiple Access (OFDMA) mode. The plurality of transmitting network apparatuses may be configured to perform constellation scrambling on symbols to be transmitted using a predetermined scrambling sequence. The plurality of transmitting network devices may be further configured to synchronize the use of the sequence, for example by advancing the sequence for each available subcarrier, such that the receiving device may view the payload as if it were transmitted by a single transmitter. Thus, these multiple transmissions can be descrambled using only one instance of the sequence generator.

In one embodiment of the disclosed method and apparatus, the network is configured to operate in an OFDMA mode where reservation requests are aggregated from multiple (up to 16) nodes that simultaneously transmit payload symbols dedicated to the Network Coordinator (NC). The individual transmitters use only a subset of the subcarriers which have been mutually exclusively preassigned to the individual transmitters. By having synchronized carrier frequencies and having the signals arrive at the NC at the same time, the joint orthogonality of all transmitted subcarriers is preserved. That is, the NC receives a apparently normal payload whose demodulated subcarriers can then be re-divided to recover individual reservation requests.

According to an embodiment of the disclosed method and apparatus, a communication network system comprises: a network device configured to transmit a quadrature amplitude modulation symbol on a subcarrier of a set of subcarriers available for orthogonal frequency division multiple access; wherein the network device is configured to perform a constellation scrambling operation on the quadrature amplitude modulation symbols, the constellation scrambling operation comprising: initializing the sequencer with a predetermined seed; and advancing the sequence generator for each subcarrier preceding the subcarrier while processing the set of available subcarriers in a predetermined order, and scrambling the quadrature amplitude modulation symbols using sequence elements generated by the sequence generator.

Other features and aspects of the disclosed method and apparatus will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example only, the features in accordance with embodiments of the disclosed method and apparatus. The summary is not intended to limit the scope of the claimed invention, which is defined only by the appended claims.

Brief Description of Drawings

The disclosed methods and apparatus in accordance with one or more various embodiments are described in detail with reference to the accompanying drawings. The drawings are provided for purposes of illustration only and merely depict typical embodiments or examples of possible embodiments of the disclosed method and apparatus. These drawings are provided to assist the reader in understanding the disclosed methods and apparatus and should not be construed as limiting the breadth, scope, or applicability of the claimed invention. It should be noted that for simplicity and ease of illustration, the drawings are not necessarily drawn to scale.

FIG. 1 illustrates an example home network in which embodiments of the disclosed methods and apparatus may be implemented.

Fig. 2 illustrates a constellation diagram showing a coding scheme of 16-QAM.

Fig. 3 illustrates frequency bands that may be used for OFDMA in accordance with embodiments of the disclosed method and apparatus.

Fig. 4 illustrates an OFDM encoding module that may be used in accordance with embodiments of the disclosed method and apparatus.

FIG. 5 illustrates scrambling operations in accordance with embodiments of the disclosed method and apparatus.

Fig. 6 illustrates a plurality of orthogonal frequency subcarriers that have been associated with elements of a pseudorandom noise sequence.

Figure 7 illustrates descrambling operations in accordance with embodiments of the disclosed method and apparatus.

Figure 8 illustrates a descrambling and decoding module of a network device for receiving a signal during an OFDMA communication period according to embodiments of the disclosed method and apparatus.

Fig. 9 illustrates a general constellation scrambling process that may be implemented in embodiments of the disclosed methods and apparatus.

FIG. 10 illustrates a more specific scrambling process that may be implemented in embodiments of the disclosed method and apparatus.

FIG. 11 illustrates a pseudo-random sequence generator that may be implemented in embodiments of the disclosed method and apparatus.

FIG. 12 illustrates an example computing module that may be used in implementing various features of embodiments of the disclosed methods and apparatus.

The drawings are not intended to be exhaustive or to limit the disclosed methods and apparatus to the precise forms disclosed. It is to be understood that the disclosed method and apparatus may be practiced with modification and alteration, and that the claimed invention should be limited only by the claims and the equivalents thereof.

Detailed Description

Before describing the disclosed method and apparatus in detail, it is useful to describe several example environments in which the disclosed method and apparatus may be implemented. Fig. 1 is a block diagram illustrating one such example environment including a home cable network. The example of a home environment shown in fig. 1 also includes examples of equipment and other electronic devices or nodes that may be found in a typical home networking environment, such as the network defined by MoCA. The network of fig. 1 includes a set-top box 111 and a Television (TV)110 in a master bedroom 115, bedroom 114 and family room 113. Also, a typical home network may include computing systems such as desktop computing system 117 and peripherals as illustrated in den 113, and laptop computer 118 as illustrated in kitchen 112. Other content devices or network devices may also be provided.

In many communication networks, Orthogonal Frequency Division Multiplexing (OFDM) is used to transmit physical layer (PHY) packets. In OFDM, data is modulated onto a plurality of frequency subcarriers. Each subcarrier is modulated using Quadrature Amplitude Modulation (QAM). In QAM, the phases of two carriers of the same frequency are modulated. The two subcarriers are referred to as a quadrature (Q) component and an in-phase (I) component. For example, FIG. 2 illustrates a coding scheme for 16-QAM. As shown, both the quadrature and in-phase components may assume any of four different phases for a total of 16 different symbols. By representing this coding scheme with Q and I as axes of curves, a constellation can be obtained. The operation of the QAM symbols is then described in terms of the operations performed on their respective constellation points. For example, rotating point 150 by 180 would map it to point 151, equivalent to multiplying the quadrature component by-1 and the in-phase component by-1. As shown, a constellation comprising two points would be equivalent to Binary Phase Shift Keying (BPSK). Although BPSK requires only one carrier, it will be understood that BPSK is encompassed unless quadrature amplitude modulation is otherwise stated herein.

The MoCA network includes a plurality of client nodes, e.g., TVs 110, set-top boxes 111, and computers 117, 118. It should be noted that the TV 110, set top box 111 and computers 117, 118 are configured with communication devices, allowing these devices to operate as client nodes on a MoCA network. Initially, one of the client nodes is automatically selected as a Network Coordinator (NC) when the MoCA network is established. To create a system to allocate network bandwidth, the NC schedules communications to occur on the network. The NC transmits scheduling to each client node in a "media access packet" (MAP). Each MAP is an information packet. The NC sends a MAP during each "MAP cycle". In order for the NC to perform these time-scheduled tasks, the NC provides the network devices with an opportunity to send "reservation requests" (RRs) that contain requests for certain amounts of bandwidth at a time. The time required to receive these RRs increases with the size of the network. For example, if the MAP period is 1000 μ s and each RR requires 17 μ s, 255 μ s or about 25% of the channel time would be required to receive the RR alone from 15 non-control nodes in a 16 node network.

The disclosed methods and apparatus are sometimes referred to in this example environment. The description for this environment is provided to allow various features and embodiments of the disclosed method and apparatus to be described as one example in the context of a particular application. After reading this description, it will be apparent to those skilled in the art how the disclosed methods and apparatus can be implemented in different and alternative environments.

Fig. 3 illustrates frequency bands that may be used for OFDMA in accordance with embodiments of the disclosed method and apparatus. In this band, a plurality of frequency subcarriers 201 or "tones" (represented by the upward pointing arrows) are provided for OFDM communication. In some embodiments, a portion of tone 202 (denoted as an "X" above the tone) may be determined to be unavailable for OFDM communications, e.g., because the signal falls outside of a reserved bandwidth of subcarriers defined by the system as available bandwidth or for other users. Thus, a subset of the subcarriers within the band may be used for the subcarriers of OFDM (subcarriers not labeled "X"). In an OFDMA communication environment, additional subsets of available subcarriers are allocated to network nodes for OFDMA communication. These network nodes may then transmit simultaneously on their allocated subcarriers. For example, the portion of subcarriers allocated to node "a" 203 is labeled "a" and the portion of subcarriers allocated to node "B" 204 is labeled "B", while the subcarriers remaining available to the other node 205 are not labeled. In some embodiments, the network coordinator or controller may perform the division of the available subcarriers into node-specific parts, for example, during the node admission process. In other embodiments, such as those lacking a network controller, the allocation of available subcarriers to network nodes may be mediated by one another.

In some communication networks, OFDMA may be used for all transmission types, e.g., allowing a large number of network devices to share a common communication medium, e.g., in advanced networks. In other communication networks, OFDMA may be used for a particular transmission type. For example, OFDMA may be used for network transmissions that require information from a particular network node for scheduling and house care purposes. Using the MoCA network as an example, OFDMA may be used to send RRs during the RR period of a MAP cycle, thereby reducing the duration of the RR period and freeing up time for other network communications.

In some communication networks, different modulation schemes may be assigned to different available subcarriers. For example, different schemes may be used because communications on different subcarriers may have varying propagation or signal characteristics. For example, the first subcarrier 206 may provide a signal-to-noise ratio (SNR) that can support 1024-QAM, while the second subcarrier may have a large noise level, or reduced allowed signal strength, so that it can maintain only 2-QAM (i.e., BPSK). Thus, in some embodiments, it is not necessary that each subcarrier have the same modulation scheme, and different subcarriers may be assigned different modulation schemes. For example, the network medium may be periodically archived and the available subcarriers may be assigned different QAM modulation schemes based on these archives.

In such embodiments, different nodes may require different numbers of subcarriers even though OFDMA is reserved for transmission of house care or maintenance data exchanges, such as RRs, where the packet length is relatively constant between different nodes. For example, if the sub-carriers allocated to B204 for OFDMA support a higher QAM modulation rate, e.g., 512-QAM, while the sub-carriers allocated to a 203 do not support such a high rate, a allocates a larger number of sub-carriers, as described above.

Fig. 4 illustrates an OFDM encoding module that may be used in accordance with embodiments of the disclosed method and apparatus. In this embodiment, the encoding module 249 receives the input bitstream 250. The input bitstream 250 may represent, for example, a PHY packet. The encoding module 249 converts the serial bit stream into a parallel stream using the serial-to-parallel module 251. The parallel stream is then shown as QAM module 252, which may include a plurality of QAM encoding modules 257. In some embodiments, QAM encoding module 275 may present for each available subcarrier. Thus, in these embodiments, when the network node uses OFDMA for communication, not all available QAM modules may be used. Instead, the network node may only use QAM blocks corresponding to a subset of the allocated available subcarriers. In other embodiments, serial-to-parallel module 251 and plurality of QAM modules 257 are replaced with a single QAM encoding module that performs QAM encoding of bit stream 250 onto the used subcarriers in sequence.

After QAM encoding, an output symbol stream 253 comprising a plurality of QAM symbols and comprising OFDM symbols is provided to a scrambler module 254. The scrambler module 254 uses the output 256 of the sequence generator 255 to perform constellation scrambling operations on the received QAM symbols, as described below with reference to fig. 5. In some embodiments, the sequence generator module 255 comprises a pseudorandom noise sequence generator and the output 256 comprises a pseudorandom noise sequence. The scrambled symbol stream 257 is then provided for further use by the transmitter.

FIG. 5 illustrates scrambling operations in accordance with embodiments of the disclosed method and apparatus. In some embodiments, a common pseudo-random sequence for constellation scrambling is provided to respective network devices that transmit simultaneously during OFDMA communications. In one such embodiment, the pseudo-random sequence is initialized with a common seed such that each network device generates the same sequence. Also, according to one embodiment, the subcarriers available for OFDMA communications are indexed according to an indexing scheme common among the network nodes. In this embodiment, at the start of the constellation scrambling process (step 280), starting with the first OFDM symbol and the first subcarrier in the frequency range, the transmitting network device checks the current subcarrier to determine if the subcarrier is available for OFDMA communications (step 286). If the subcarrier is available, the device determines whether the current subcarrier is used by the device for OFDMA communication (step 281) (i.e., the subcarrier will transmit a QAM symbol on the current subcarrier). If so, the node obtains the latest element of the pseudo-random sequence (step 282) and scrambles the QAM symbols on the used subcarriers using the obtained element of the pseudo-random sequence (step 283). After step 283, or after step 281, if the subcarrier is not used, the apparatus clocks a noise generator to advance the pseudo-random sequence to the next element (step 284). In step 287, the apparatus determines whether the current subcarrier is the last subcarrier of the current symbol. In the illustrated embodiment, this step is performed after step 284 if it is determined in step 286 that the current subcarrier is not available. If step 287 determines that the current subcarrier is not the last subcarrier of the current symbol, the network device proceeds to the next subcarrier (step 288) and the method repeats from step 286. On the other hand, if the subcarrier is the last subcarrier, the apparatus determines whether the current symbol is the last symbol (step 285). If not, the apparatus proceeds to the first subcarrier of the next symbol and the method repeats again from step 286. If the current sign bit is the last sign, then all the signs in the message are scrambled and the method ends.

Thus, if the method is followed by a network device that transmits using OFDMA, then the two network devices do not use the same pseudo-random sequence elements to scramble the symbols. For example, a network device transmitting on a first subcarrier would be the only device using a first element of a pseudo-random noise sequence, a network device transmitting on a second subcarrier would be the only device using a second element of a pseudo-random noise sequence, and so on. This is illustrated in fig. 6, where each available subcarrier effectively has a unique sequence element s (n). This occurs because each network device advances the sequence generator for each available subcarrier, even those network devices that are not in use. In other embodiments, such as the embodiment illustrated with reference to fig. 6, each available subcarrier may be allocated.

Thus, the receiving network device looks at the transmitted payload as if it were transmitted by a single transmitter, and can descramble the received symbols using a single sequence generator. In some embodiments, the receiving network device processes in a manner similar to fig. 5. This is illustrated in fig. 7. When the method starts, the receiving network device provides its sequencer with the same initial seed as the transmitting network device. The decoding method then starts (step 290), starting with the first received OFDM symbol and the first subcarrier in the frequency band. As described herein, the OFDM symbol on the receiver side in this embodiment includes an OFDM symbol that is a combination of a plurality of OFDM symbols transmitted by a plurality of transmission apparatuses using OFDMA. Similar to the scrambling process, the descrambling process checks the current subcarrier (step 296) to determine if it is available for OFDMA and, if so, whether the subcarrier is used (i.e., carries QAM symbols) (step 291). If the subcarrier is used, the receiving device obtains the latest bits from the scrambling sequence (step 292) and descrambles the QAM symbols on the used subcarrier (step 293). If the subcarrier is available but not used in step 291 or after descrambling the subcarrier in step 293, then the receiving device clocks a noise generator (step 294). Continuing the descrambling process, the receiving device continues with the subcarriers of the band (steps 298 and 297) and proceeds in a manner similar to the process implemented by the transmitting device for each OFDM symbol (steps 299 and 295). After the method ends, the receiving network device has descrambled all received symbols from a plurality of transmitting devices contained in the OFDMA transmission period. In some embodiments, this avoids the need for the receiving network device to reserve multiple sequencers, since the receiving network device does not have to reserve a separate sequencer for each transmitting device to descramble communications for each transmitting device. In particular embodiments, the receiving network device may include a network controller, and the QAM symbols received during the OFDMA period may include an RR of the transmitting device. Thus, the network controller may then use the request to schedule allocation of bandwidth during the upcoming MAP and to transmit responses to the various network devices according to their allocated times.

Figure 8 illustrates a descrambling and decoding module of a network device for receiving signals during OFDMA communications in accordance with embodiments of the disclosed method and apparatus. In this embodiment, the receiving module 300 obtains a scrambled symbol stream 307. The scrambled symbol stream 307 typically comprises a plurality of QAM symbols transmitted on a corresponding plurality of used subcarriers. These used subcarriers represent the total number of subcarriers used by the network device to transmit individually during OFDMA communication. The scrambled symbol stream 307 is provided to a descrambling module 304 for constellation descrambling. As described herein, because the transmitting network devices are able to synchronize their use of the sequence generators, the receiving network devices may descramble the received stream 307 and output the sequence 306 using a single sequence generator 305. The descrambled symbol stream 303 may then be provided to a plurality of QAM decoders 307, making up QAM decoding module 302 for decoding. Once the symbols are decoded, they may be distributed and output by the distribution module 301 as a plurality of bit streams 308, one for each transmitting network device, according to their corresponding transmitting network device.

Fig. 9 illustrates a general constellation scrambling process that may be implemented in embodiments of the disclosed methods and apparatus. In the scrambling process, QAM symbol 320c (n) may be represented by a pair comprising an in-phase component and a quadrature component, c (n) ═ { i (n), q (n) }. In one scrambling process, the in-phase 321, I (n), and quadrature 322, Q (n) components of the symbol are transformed 324 and 325, respectively. In these transformations, a known sequence element, such as a pseudo-random sequence 323, may be used to descramble the symbols including the inverse operation using the same sequence element. After transformation, the scrambled symbols C (n) ' 328 include a scrambled in-phase component 326, I (n) ', and a scrambled quadrature component 327, Q (n) '.

FIG. 10 is a block diagram of components used to perform a process in accordance with embodiments of the disclosed method and apparatus. In this process, the predetermined sequence 340 is provided to a mapping function 342. In one embodiment, the bit stream 340 includes pseudo-random sequences of 1's and 0's. The mapping function 342 maps 1 to-1 and 0 to 1, forming pseudo-random sequences of 1 and-1. Input symbol stream 341 is coupled to a symbol module 343 to obtain QAM symbols. Multiplier 344 multiplies the in-phase and quadrature components of the symbol with the result of mapping function 342. If the current element of the pseudo-random sequence is 1, the mapping function 342 returns-1 and the in-phase and quadrature components are inverted, corresponding to a 180 rotation (as viewed on the constellation). Also, if the current element of the pseudorandom sequence is 0, the mapping function 342 returns a 1, generating an identification function, keeping the in-phase and quadrature components unchanged. The output of multiplier 344 is a scrambled symbol stream 345. In this particular scrambling process, as well as other scrambling processes, the scrambling function is the inverse of itself. In other words, providing scrambled symbol stream 345 to symbol module 343 in place of input symbol stream 341 will produce the original un-scrambled stream 341 output from multiplier 344, assuming that the pseudorandom sequence 340 begins at the original initial value.

FIG. 11 illustrates a pseudo-random sequence generator that may be implemented in embodiments of the disclosed method and apparatus. The figure illustrates a method for generatingA sequence generator forming a 15-order pseudo-random noise sequence (PN-15(n)) with a generator polynomial of X¹⁵+ X + 1. In a particular embodiment, each network device in the communication network has such a sequencer. At the beginning of the OFDMA transmission period, each transmitter initializes the shift register 370 with a predetermined seed. For example, in a particular embodiment, shift register 370 is initialized with the 15 th least significant bit of 0x3EA 9. In some embodiments, the current element of the pseudorandom sequence comprises a current occupancy A₀E.g., the first element of the pseudorandom sequence will comprise the least significant bit of the seed. When the sequencer is clocked, the shift register generates a new A₁₄As A₀+A₁Discard A₀From A to A_nMove to A_n-1. Thus, the sequence is generated in a deterministic manner, but it can be shown that all 2's are generated with a uniform distribution¹⁵Possible 15-bit combinations. Thus, the sequence looks like noise as it progresses.

As described herein, because each transmitting network device involved in the OFDMA period initializes their generator with the same seed and clocks their generator for each available subcarrier, not just for all of their subcarriers, the various transmitting network devices are able to synchronize their use of pseudorandom sequences for QAM symbol scrambling. Thus, the receiving network device is able to descramble all received QAM symbols during an OFDMA period using one sequence generator and descrambling module without having to maintain separate descrambling modules for each transmitting network device.

As used herein, the term module may describe a given unit of functionality that may be performed in accordance with one or more embodiments of the disclosed methods and apparatus. As used herein, a module may be implemented using any form of hardware, software, or combination thereof. For example, one or more processors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs, logic components, software routines or other mechanisms may be implemented to form modules. In implementations, the various modules described herein may be implemented as discrete modules or the functions and features described may be in one or more portions or all of one or more modules. In other words, various features and functions described herein may be implemented in a given application after reading this specification, and may be implemented in one or more separate or common modules, in various combinations and permutations, as would be apparent to one skilled in the art. Even though various features or elements of functionality may be described separately or claimed as separate modules, those skilled in the art will appreciate that such features and functionality may be shared among one or more common software and hardware components, and that such description will not require or imply the use of separate hardware or software components to implement such features or functionality.

If the components or modules of the disclosed methods and apparatus are implemented in whole or in part using software in one embodiment, these software components may be implemented to work with a computing or processing module capable of performing the functions described herein. FIG. 12 illustrates one such example computing module. Various embodiments are described in terms of this example computing module 400. After reading this description, it will become apparent to one skilled in the art how to implement the disclosed methods and apparatus using other computing modules or architectures.

Referring now to FIG. 12, computing module 400 may represent one or more processors, controllers, control modules, or other processing devices, such as processor 404, or desktop, laptop, and notebook computers, for example; handheld computing devices (PDAs, smart phones, cellular phones, palmtop computers, etc.); a host, a supercomputer, a workstation or a server; or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment. In one embodiment, the computing module may be present in other electronic devices such as, for example, digital cameras, navigation systems, cellular telephones, portable computing devices, modems, routers, WAPs, terminal boxes that may include some form of processing capability, and other electronic devices.

Processor 404 may be implemented using a general or special purpose processing engine such as, for example, a microprocessor, controller or other control logic. In the depicted example, processor 404 is connected to bus 402, although any communication medium may be used to facilitate interaction with or external communication with other elements of computing module 400.

The computing module 400 also includes one or more memory modules, referred to herein simply as main memory 408. For example, Random Access Memory (RAM) or other dynamic memory may be preferably used for storing information and instructions to be executed by processor 404. Main memory 408 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 404. Computing module 400 may similarly include a read only memory ("ROM") or other static storage device coupled to bus 402 for storing static information and instructions for processor 404.

Computing module 400 may also include one or more various forms of information storage mechanism 410, which may include, for example, a media drive 412 and a storage unit interface 420. The media drive 412 may include a drive or other mechanism to support fixed or removable storage media. For example, a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a CD or DVD drive (R or RW), or other removable or fixed media drives may be provided. Thus, storage media 414 may include, for example, a hard disk, floppy disk, magnetic tape, cartridge, optical disk, CD or DVD, or other fixed or removable medium that is read by, written to, or accessed by media drive 412. As these examples illustrate, the storage media 414 may include a computer-usable storage medium having stored therein computer software or data.

In alternative embodiments, information storage mechanism 410 may include other similar means for allowing computer programs or other instructions or data to be loaded into computing module 400. Such means may include, for example, a fixed or removable storage unit 422 and an interface 420. Examples of such a storage unit 422 and interface 420 may include a program cartridge and cartridge interface, a removable memory (e.g., a flash memory or other removable memory module) and memory slots, PCMCIA slots and cards, and other fixed or removable storage units 422 and interfaces 420 that allow software and data to be transferred from the storage unit 422 to the computing module 400.

Computing module 400 may also include a communications interface 424. Communication interface 424 may be used to allow software and data to be transferred between computing module 400 and external devices. Examples of communication interface 424 may include a modem or soft modem, a network interface (e.g., Ethernet, network interface card, WiMedia, IEEE 802.XX, or other interface), a communication port (e.g., such as a USB port, IR port, RS232 port, BluetoothAn interface, or other port), or other communication interface. Software and data transferred via communications interface 424 are typically carried on signals which may be electronic, electromagnetic (including optical) or other signals capable of being exchanged by a given communications interface 424. These signals may be provided to communications interface 424 via a channel 428. This channel 428 may carry signals and may be implemented using a wired or wireless communication medium. Some examples of a channel may include a telephone line, a cellular link, an RF link, an optical link, a network interface, a local or wide area network, and other wired or wireless communication channels.

In this document, the terms "computer program medium" and "computer usable medium" are used to generally refer to media such as, for example, memory 408, storage unit 420, media 414 and channel 428. In addition, various embodiments presented herein are described in terms of block diagrams, flow charts and other illustrations. It will be apparent to those skilled in the art upon reading this document that the illustrated embodiments and various alternative embodiments thereof may be implemented without limitation to the illustrated examples. For example, block diagrams and their corresponding descriptions should not be read to imply a particular architecture or structure. Therefore, the particular embodiments disclosed herein should not be taken as limiting the scope of the claimed invention, which is defined in the following claims and not as limiting the specific embodiments provided herein.

Claims (18)

1. A method of communication transmission using orthogonal frequency division multiple access over a network, comprising:

providing a set of available subcarriers for orthogonal frequency division multiple access for a plurality of transmitting network devices;

providing corresponding elements of a pseudo-random noise sequence for each subcarrier of the set of available subcarriers;

allocating a subset of the set of available subcarriers to each transmitting network device;

a transmitting network means of said plurality of means maps a packet onto a plurality of used subcarriers of said allocated subset of available subcarriers, wherein the step of mapping said packet comprises mapping said packet onto a plurality of quadrature amplitude modulation symbols to be transmitted on the used subcarriers;

the transmitting network means performing a predetermined transformation on the orthogonal amplitude modulation symbols using elements of the pseudo random noise sequence corresponding to the used subcarriers;

the transmitting network device transmits the transformed symbols to the receiving network device.

2. A method as defined in claim 1, wherein the steps of providing corresponding elements of the pseudo-random noise sequence and performing the predetermined transformation comprise:

the transmitting network device receiving an initial pseudo-random noise sequence element from a pseudo-random noise sequence generator, the initial pseudo-random noise sequence element corresponding to a first available subcarrier and transforming the symbol to be transmitted on the first available subcarrier if the first available subcarrier is the used subcarrier; and is

The transmitting network device advances the pseudo random noise generator to receive a next element of the pseudo random noise sequence corresponding to a next available subcarrier and transforms the symbol to be transmitted on the next available subcarrier if the next available subcarrier is the used subcarrier.

3. A method as claimed in claim 3, wherein the step of the transmitting network device advancing the pseudo random noise generator is repeated until the symbol to be transmitted on the last used subcarrier has been transformed.

4. A method as defined in claim 1, wherein the pseudo-random noise sequence comprises a PN-15 sequence.

5. A method as defined in claim 4, wherein the step of performing the predetermined transformation comprises rotating the quadrature amplitude modulation symbol by 180 ° if an element of a pseudo random noise sequence is "1", and not changing the quadrature amplitude modulation symbol if the element of the pseudo random noise sequence is "0".

6. The method of claim 4, wherein the receiving network device comprises a network coordinator and wherein the packet comprises a resource reservation request packet.

7. A communication receiving method using orthogonal frequency division multiple access on a network, comprising:

receiving a first scrambled orthogonal frequency division modulation symbol from a first transmitting network device, the first orthogonal frequency division modulation symbol comprising a first plurality of scrambled orthogonal amplitude modulation symbols transmitted on a corresponding first plurality of used subcarriers allocated to the first transmitting network device;

receiving a second scrambled orthogonal frequency division modulation symbol from a second transmitting network device, the second orthogonal frequency division modulation symbol comprising a second plurality of scrambled orthogonal amplitude modulation symbols transmitted on a corresponding second plurality of used subcarriers allocated to the second transmitting network device;

wherein the first plurality of subcarriers and the second plurality of subcarriers are a subset of a set of available subcarriers, and wherein subcarriers of the set of available subcarriers have corresponding elements of a pseudorandom noise sequence; and

descrambling the first and second scrambled orthogonal frequency division modulation symbols, the descrambling step comprising descrambling scrambled orthogonal amplitude modulation symbols transmitted on the used subcarrier using elements of a pseudo random noise sequence corresponding to the used subcarrier.

8. The method of claim 7, wherein the step of descrambling the first and second scrambled orthogonal frequency division modulation symbols comprises receiving an initial pseudorandom noise sequence element from a pseudorandom noise sequence generator, the initial pseudorandom noise sequence element corresponding to a first available subcarrier and descrambling a symbol received on the first available subcarrier if the first available subcarrier is the used subcarrier; and

advancing the pseudo random noise generator so as to receive a next element of the pseudo random noise sequence corresponding to a next available subcarrier and descrambling a symbol received on the next available subcarrier if the next available subcarrier is the used subcarrier.

9. The method of claim 8, wherein the step of advancing the pseudo random noise generator is repeated until the symbol to be transmitted on the last used subcarrier is descrambled.

10. A method as defined in claim 7, wherein the pseudorandom noise sequence comprises a 15 th order pseudorandom noise sequence.

11. The method of claim 10, wherein the step of descrambling the scrambled quadrature amplitude modulation symbols comprises rotating the scrambled quadrature amplitude modulation symbols by 180 ° if an element of the pseudo random noise sequence is "1" and not changing the scrambled quadrature amplitude modulation symbols if the element of the pseudo random noise sequence is "0".

12. The method of claim 4, wherein the method is performed by a network coordinator and wherein the first and second scrambled orthogonal frequency division modulation symbols are contained in a resource reservation request packet.

13. A communication network system comprising:

a network device configured to transmit a quadrature amplitude modulation symbol on a subcarrier of a set of subcarriers available for orthogonal frequency division multiple access;

wherein the network device is configured to perform a constellation scrambling operation on the quadrature amplitude modulation symbols, the constellation scrambling operation comprising:

initializing the sequencer with a predetermined seed; and

while processing the set of available subcarriers in a predetermined order, advancing the sequence generator for each subcarrier preceding the subcarrier and scrambling the quadrature amplitude modulation symbols using sequence elements generated by the sequence generator.

14. The system of claim 13, further comprising:

a second network device configured to transmit a second quadrature amplitude modulation symbol on a second subcarrier of the set of available subcarriers;

wherein the second network device is configured to perform a second constellation scrambling operation on the second quadrature amplitude modulation symbol, the second constellation scrambling operation comprising:

initializing a second sequence generator with the predetermined seed; and

while processing the set of available subcarriers in the predetermined order, advancing the second sequence generator for each subcarrier preceding the second subcarrier and scrambling the second quadrature amplitude modulation symbol using a second element of a second sequence generated by the second sequence generator.

15. The system of claim 14, further comprising:

a receiving network device configured to receive the first and second scrambled quadrature amplitude modulation symbols;

wherein the receiving network apparatus is configured to perform a constellation descrambling operation on the first and second scrambled quadrature amplitude modulation symbols, the constellation descrambling operation comprising:

initializing a third sequence generator with the predetermined seed; and

while processing the set of available subcarriers in the predetermined order, advancing the third sequence generator for respective subcarriers preceding the first subcarrier and descrambling the first quadrature amplitude modulation symbol using the first element, advancing the third sequence generator for respective subcarriers preceding the second subcarrier and descrambling the second quadrature amplitude modulation symbol using the second element.

16. A network device configured to transmit quadrature amplitude modulation symbols on subcarriers of a set of subcarriers available for orthogonal frequency division multiple access, the network device comprising a computer readable medium having computer executable program code embodied on the computer readable medium, wherein the computer executable code is configured to cause the network device to perform the steps of:

performing a constellation scrambling operation on the quadrature amplitude modulation symbols to form scrambled quadrature amplitude modulation symbols, the constellation scrambling operation comprising:

initializing the sequencer with a predetermined seed; and

while processing the set of available subcarriers in a predetermined order, advancing the sequence generator for each subcarrier preceding the subcarrier and scrambling the quadrature amplitude modulation symbols using sequence elements generated by the sequence generator.

17. The network device of claim 16, wherein the computer-executable program code is further configured to cause the device to transmit the scrambled quadrature amplitude modulation symbols to a receiving network device.

18. The network device of claim 17, wherein the receiving network device comprises a network coordinator, the sequence comprises a pseudo-random sequence of order 15, and the quadrature amplitude modulation symbols comprise code symbols of a resource reservation request.