Patent ID: 12192893

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of novel embodiments depicted in the accompanying drawings. However, the amount of detail offered is not intended to limit anticipated variations of the described embodiments; on the contrary, the claims and detailed description are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present teachings as defined by the appended claims. The detailed descriptions below are designed to make such embodiments understandable to a person having ordinary skill in the art.

Embodiments may comprise an orthogonal frequency division multiplexing (OFDM) system operating in the 1 GHz and lower frequency bands. In many embodiments, physical layer logic may implement a new preamble structure with a new signal field. Some embodiments may provide, e.g., indoor and/or outdoor “smart” grid and sensor services. For example, some embodiments may provide sensors to meter the usage of electricity, water, gas, and/or other utilities for a home or homes within a particular area and wirelessly transmit the usage of these services to a meter substation. Further embodiments may utilize sensors for home healthcare, clinics, or hospitals for monitoring healthcare related events and vital signs for patients such as fall detection, pill bottle monitoring, weight monitoring, sleep apnea, blood sugar levels, heart rhythms, and the like. Embodiments designed for such services generally require much lower data rates and much lower (ultra low) power consumption than devices provided in IEEE 802.11n/ac systems.

Some embodiments reuse the IEEE 802.11n/ac system with new features that meet these lower data rate and ultra low power consumption requirements to reuse hardware implementations and to reduce implementation costs. In some embodiments, the new preamble structure may use a short training field (STF) and a long training field (LTF) from the IEEE 802.11ac and IEEE 802.11ag systems, reducing the cost of implementations. Further embodiments accommodate multiple streams. Several embodiments do not implement legacy training fields and legacy signatures and do not implement multi-user, Multiple Input, Multiple Output (MIMO). And some embodiments employ beamforming.

In the frequency bands of 1 GHz and lower, the available bandwidth is restricted, thus an IEEE 802.11n/ac type system that uses bandwidths of 20, 40, 80 and 160 MHz may not be practicable in some geographic regions. In many embodiments, the systems have bandwidths on the order of approximately 1 to 10 MHz. In several embodiments, an 802.11n/ac type system may be down-clocked to achieve lower bandwidths. For instance, many embodiments are down-clocked by N, such as 20 MHz divided by N, where N could take on values of 2, 4, 8, 10, and 20 (providing 10, 5, 2.5, 2, and 1 MHz bandwidth operation). Further embodiments are down-clocked by N, such as 160 MHz divided by N, where N could take on values of 10, 20, 40, 80, and 160 (providing 16, 8, 4, 2, and 1 MHz bandwidth operation). In several embodiments, the bandwidths may also be based on the tone count for those IEEE 802.11ac systems. In some embodiments, the tone counts may be the same as those IEEE 802.1 lac systems. In other embodiments, the tone counts may be different from those IEEE 802.11ac systems, removing, for example, tone counts that are not unnecessary at the lower bandwidths.

Embodiments of the preamble structure may implement the new signal field, 11ah-SIG. The preamble structure may define an STF and an LTF to train the antennas for one stream operation, followed by the signal field and the data payload. In some embodiments, the signal field may be preceded by a guard interval (GI) and followed by additional LTFs to accommodate additional multiple input, multiple output (MIMO) streams. Other embodiments do not comprise the additional LTFs because they communicate via a single stream.

Logic, modules, devices, and interfaces herein described may perform functions that may be implemented in hardware and/or code. Hardware and/or code may comprise software, firmware, microcode, processors, state machines, chipsets, or combinations thereof designed to accomplish the functionality.

Embodiments may facilitate wireless communications. Some embodiments may integrate low power wireless communications like Bluetooth®, wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), wireless personal area networks (WPAN), cellular networks, Institute of Electrical and Electronic Engineers (IEEE) IEEE 802.11-2007, IEEE Standard for Information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (http://standards.ieee.org/getieee802/download/802.11-2007.pdf), communications in networks, messaging systems, and smart-devices to facilitate interaction between such devices. Furthermore, some wireless embodiments may incorporate a single antenna while other embodiments may employ multiple antennas.

Turning now toFIG.1, there is shown an embodiment of a wireless communication system1000. The wireless communication system1000comprises a communications device1010that is wire line or wirelessly connected to a network1005. The communications device1010may communicate wirelessly with a plurality of communication devices1030,1050, and1055via the network1005. The communications devices1010,1030,1050, and1055may comprise sensors, stations, access points, hubs, switches, routers, computers, laptops, notebooks, cellular phones, PDAs (Personal Digital Assistants), or other wireless-capable devices. Thus, communications devices may be mobile or fixed. For example, the communications device1010may comprise a metering substation for water consumption within a neighborhood of homes. Each of the homes within the neighborhood may comprise a communications device such as the communications device1030and the communications device1030may be integrated with or coupled to a water meter usage meter. Periodically, the communications device1030may initiate communications with the metering substation to transmit data related to water usage. Furthermore, the metering station or other communications device may periodically initiate communications with the communications device1030to, e.g., update firmware of the communications device1030. In other embodiments, the communications device1030may only respond to communications and may not comprise logic that initiates communications.

In further embodiments, the communications device1010may facilitate data offloading. For example, communications devices that are low power sensors may include a data offloading scheme to, e.g., communicate via Wi-Fi, another communications device, a cellular network, or the like for the purposes of reducing power consumption consumed in waiting for access to, e.g., a metering station and/or increasing availability of bandwidth. Communications devices that receive data from sensors such as metering stations may include a data offloading scheme to, e.g., communicate via Wi-Fi, another communications device, a cellular network, or the like for the purposes of reducing congestion of the network1005.

The network1005may represent an interconnection of a number of networks. For instance, the network1005may couple with a wide area network such as the Internet or an intranet and may interconnect local devices wired or wirelessly interconnected via one or more hubs, routers, or switches. In the present embodiment, network1005communicatively couples communications devices1010,1030,1050, and1055.

The communication devices1010and1030comprise memory1011and1031, and medium access control (MAC) sublayer logic1018and1038, respectively. The memory1011,1031such as dynamic random access memory (DRAM) may store the frames, preambles, and preamble structures1014and1034, or portions thereof. The frames, also referred to as MAC layer protocol data units (MPDUs), and the preamble structures1014and1034may establish and maintain synchronized communications between the transmitting device and the receiving device. The preamble structures1014and1034may also establish the communications format and rate. In particular, preambles generated or determined based upon the preamble structures1014and1034may train, e.g., the antenna arrays1024and1044to communicate with each other, establish the modulation and coding scheme of the communications, the bandwidth or bandwidths of the communications, the length of the transmission vector (TXvector), the application of beamforming, and the like.

The MAC sublayer logic1018,1038may generate the frames and the physical layer (PHY) logic1019,1039may generate physical layer data units (PPDUs). More specifically, the frame builders1012and1032may generate frames and the data unit builders1013and1033may generate PPDUs. The data unit builders1013and1033may generate PPDUs by encapsulating payloads comprising the frames generated by frame builders1012and1032. In the present embodiment, the data unit builders1013and1033may encapsulate the frames with preambles based upon preamble structures1014and1034, respectively, to prefix the payloads to be transmitted over one or more RF channels. The function of a data unit builder, such as the data unit builder1013or1033, is to assemble groups of bits into code words or symbols that make up the preambles as well as the payloads so the symbols can be converted into signals to transmit via antenna arrays1024and1044, respectively.

Each data unit builder1013,1031may supply a preamble structure1014,1034comprising a signal field1015,1035and store the preambles generated based upon the preamble structure1014,1034in the memory1011,1031while the preambles are being generated and/or after the preambles are generated. In the present embodiment, the preamble structure1014,1034may comprise one short training field (STF) and one long training field (LTF) prior to the signal field1015,1035and the data payload. The STF and the LTF may train the antenna arrays1022and1042to communicate with each other by making measurements related to communications such as measurements related to relative frequency, amplitude, and phase variations between quadrature signals. In particular, the STF may be used for packet detection, automatic gain control, and coarse frequency estimation. The LTF may be used for channel estimation, timing, and fine frequency estimation for a spatial channel.

The signal field1015,1035provides data related to establishing communications including, for example, bits representing the modulation and coding scheme MCS, bandwidth, length, beamforming, space time block coding (STBC), coding, aggregation, short guard interval (Short GI), cyclic redundancy check (CRC), and a tail. In some embodiments, for instance, the signal field1015,1035may comprise an MCS including Binary Phase-Shift Keying (BPSK) with a coding rate of ½ or a 256-point constellation, Quadrature Amplitude Modulation (256-QAM) with a coding rate of ¾. In further embodiments, the signal field1015,1035includes a modulation technique such as Staggered-Quadrature, Phase-Shift Keying (SQPSK). In many embodiments, the MCS establishes communication with 1 to 4 spatial streams.

In several embodiments, the signal field1015,1035may comprise bandwidths including 20 Megahertz (MHz) divided by N, 40 MHz divided by N, 80 MHz divided by N, or 160 MHz divided by N, wherein N is an integer and the bandwidths fall between 1 and 10 MHz. For example, bandwidths may include 160 MHz divided by N, wherein N equals 160, 80, 40, 20, and 10, which results in bandwidths of 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz. In further embodiments, bandwidths may include 20 MHz divided by N, wherein N equals 2, 4, 8, 10, 16, and 20, which results in bandwidths of 1 MHz, 1.25 MHz, 2 MHz, 2.5 MHz, 5 MHz, and 10 MHz

The communications devices1010,1030,1050, and1055may each comprise a transceiver (RX/TX) such as transceivers (RX/TX)1020and1040. Each transceiver1020,1040comprises an RF transmitter and an RF receiver. Each RF transmitter impresses digital data onto an RF frequency for transmission of the data by electromagnetic radiation. An RF receiver receives electromagnetic energy at an RF frequency and extracts the digital data therefrom.FIG.1may depict a number of different embodiments including a Multiple-Input, Multiple-Output (MIMO) system with, e.g., four spatial streams, and may depict degenerate systems in which one or more of the communications devices1010,1030,1050, and1055comprise a receiver and/or a transmitter with a single antenna including a Single-Input, Single Output (SISO) system, a Single-Input, Multiple Output (SIMO) system, and a Multiple-Input, Single Output (MISO) system. The wireless communication system1000ofFIG.1is intended to represent an Institute for Electrical and Electronics Engineers (IEEE) 802.11ah system. Similarly, devices1010,1030,1050, and1055are intended to represent IEEE 802.11ah devices.

In many embodiments, transceivers1020and1040implement orthogonal frequency-division multiplexing (OFDM). OFDM is a method of encoding digital data on multiple carrier frequencies. OFDM is a frequency-division multiplexing scheme used as a digital multi-carrier modulation method. A large number of closely spaced orthogonal sub-carrier signals are used to carry data. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a modulation scheme at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.

An OFDM system uses several carriers, or “tones,” for functions including data, pilot, guard, and nulling. Data tones are used to transfer information between the transmitter and receiver via one of the channels. Pilot tones are used to maintain the channels, and may provide information about time/frequency and channel tracking. Guard tones may be inserted between symbols such as the STF and LTF symbols during transmission to avoid inter-symbol interference (ISI), which might result from multi-path distortion. These guard tones also help the signal conform to a spectral mask. The nulling of the direct component (DC) may be used to simplify direct conversion receiver designs.

In one embodiment, the communications device1010optionally comprises a digital beam former (DBF)1022, as indicated by the dashed lines. The DBF1022transforms information signals into signals to be applied to elements of an antenna array1024. The antenna array1024is an array of individual, separately excitable antenna elements. The signals applied to the elements of the antenna array1024cause the antenna array1024to radiate one to four spatial channels. Each spatial channel so formed may carry information to one or more of the communications devices1030,1050, and1055. Similarly, the communications device1030comprises a transceiver1040to receive and transmit signals from and to the communications device1010. The transceiver1040may comprise an antenna array1044and, optionally, a DBF1042. In parallel with digital beam forming, the transceiver1040is capable of communicating with IEEE 802.11ah devices.

FIG.1Adepicts an embodiment of a physical layer protocol data unit (PPDU)1060with a preamble structure1062for establishing communications between wireless communication devices such as communications devices1010.1030,1050, and1055inFIG.1. The PPDU1060may comprise a preamble structure1062including orthogonal frequency division multiplexing (OFDM) training symbols for a single multiple input, multiple output (MIMO) stream followed by a signal field, followed by additional OFDM training symbols for additional MIMO streams, and the preamble structure1060may be followed by the data payload. In particular, the PPDU1060may comprise a short training field (STF)1064, a long training field (LTF)1066, the 11AH-SIG1068, additional LTFs1069, and data1070. The STF1064may comprise a number of short training symbols such as 10 short training symbols that are 0.8 microseconds (s) times N in length, wherein N is an integer representing the down-clocking factor from a 20 MHz channel spacing. For instance, the timing would double for 10 MHz channel spacing. The total time frame for the STF1064at a 20 MHz channel spacing is 8 μs times N.

The LTF1066may comprise a guard interval (GI) symbol and two long training symbols. The guard interval symbol may have a duration of 1.6 μs times N and each of the long training symbols may have durations of 3.2 μs times N at the 20 MHz channel spacing. The total time frame for the LTF1066at a 20 MHz channel spacing is 8 μs times N.

The 11ah-SIG1068may comprise a GI symbol at 0.8 μs times N and signal field symbols at 7.2 μs times N such as the symbols described inFIG.1C. The additional LTFs1069may comprise one or more LTF symbols for additional MIMO streams if needed at 4 μs times N at 20 MHz channel spacing. The data1070may comprise one or more MAC sublayer protocol data units (MPDUs) and may include one or more GIs. For example, data1070may comprise one or more sets of symbols including a GI symbol at 0.8 μs times N at the 20 MHz channel spacing followed by payload data at 3.2 μs times N at the 20 MHz channel spacing.

The present embodiment may comprise five allowed bandwidths such as 1 MHz, 2 MHz, 4 MHz, 8 MHz and 16 MHz. In some embodiments, the preamble generated in accordance with the preamble structure1062may be replicated into, e.g., two bandwidths such as two 1 MHz bandwidths. Once the data portion starts, replication may no longer occur and new tone allocations may be implemented. For instance, the tone allocation for the preamble may be fixed at 56 tones for the lowest bandwidth (1 MHz), may be replicated to get a total of 112 tones for the next bandwidth (2 MHz), may be replicated for a total of 224 tones for the next bandwidth (4 MHz), may be replicated again for a total of 448 tones for the next bandwidth (8 MHz), and may be replicated again for a total of 896 tones for the largest bandwidth (16 MHz). The tone allocation for the data1070may be set at 56 tones (52 data tones plus 4 pilot tones) for a 1 MHz bandwidth, 114 tones (108 tones for the data plus 6 pilot tones) for a 2 MHz bandwidth, 242 tones (234 data tones plus 8 pilot tones) for a 4 MHz bandwidth, 484 tones (468 tones for the data plus 16 pilot tones) for a 8 MHz bandwidth, and 968 tones (936 tones for the data plus 32 pilot tones) for a 16 MHz bandwidth.

FIG.1Bdepicts an alternative embodiment of a physical layer protocol data unit (PPDU)1080with a preamble structure1082for establishing communications between wireless communication devices such as communications devices1010.1030,1050, and1055inFIG.1. The PPDU1080may comprise a preamble structure1082including orthogonal frequency division multiplexing (OFDM) training symbols for a single multiple input, multiple output (MIMO) stream followed by a signal field, and the data payload may follow the preamble structure1080. In particular, the PPDU1080may comprise a short training field (STF)1064, a long training field (LTF)1066, the 11AH-SIG1068, and data1070.

FIG.1Cdepicts an embodiment of a signal field, 11AH-SIG1068for establishing communications between wireless communication devices such as communications devices1010,1030,1050, and1055inFIG.1. While the number, types, and content of the fields may differ between embodiments, the present embodiment may comprise a signal field with a sequence of bits for a modulation and coding scheme (MCS)1104parameter, a bandwidth (BW)1106parameter, a length1108parameter, a beamforming (BF)1110parameter, a space-time block coding (STBC)1112parameter, a coding1114parameter, an aggregation1116parameter, a short guard interval (SGI)1118parameter, a cyclic redundancy check (CRC)1120parameter, and a tail1122parameter.

The MCS1104parameter may comprise six bits and may designate binary phase-shift keying (BPSK), 16-point constellation quadrature amplitude modulation (16-QAM), 64-point constellation quadrature amplitude modulation (64-QAM), 256-point constellation quadrature amplitude modulation (256-QAM), quadrature phase-shift keying (QPSK), or staggered quadrature phase-shift keying (SQPSK) as a modulation format for a communication. The selections may offer one to four spatial streams for the communication. The BPSK may have a coding rate of ½. The 256-QAM may have a coding rate of ¾. And the SQPSK, also referred to as OQPSK, may have a coding rate of ½ or ¾. In some embodiments, SQPSK is an allowed modulation format on the signal and data fields to extend the range of operation of the communications devices for, e.g., outdoor sensor monitoring.

The BW1106parameter may comprise 2 bits and may involve selecting a bandwidth from four bandwidths such as 2 MHz, 4 MHz, 8 MHz, and 16 MHz. Selection of a fifth bandwidth such as 1 MHz may also be selected via another method. In other embodiments, the BW1106parameter may offer four different bandwidths that are down-clocked by an integer N from 20 MHz, 40 MHz, 80 MHz, or 160 MHz. The number N may be any integer such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, . . . .

The length1108parameter may comprise 16 bits and may describe the length of the transmit vector in octets. In some embodiments, the allowed values for the length1108parameter are in the range of 1 to 4095. The length1108parameter may indicate the number of octets in the MAC protocol data unit (MPDU) that the MAC sublayer logic is currently requesting the physical layer (PHY) device, e.g., the transceiver1020,1040inFIG.1, to transmit. The length1108parameter is used by the PHY to determine the number of octet transfers that will occur between the MAC and the PHY after receiving a request to start the transmission.

The beamforming (BF)1110parameter may comprise one bit and may designate whether or not the PHY will implement beamforming for transmission of the MPDU. The space-time block coding (STBC)1112parameter may comprise one bit and may designate whether or not to implement a space-time block coding such as Alamouti's code. And the coding1114parameter may comprise two bits and may designate whether to use binary convolutional coding (BCC) or low density parity check coding (LDPC).

The aggregation1116parameter may comprise one bit and may designate whether or not to mandate MPDU aggregation (A-MPDU). The short guard interval (SGI)1118parameter may comprise one or two bits and may designate the duration of the SGI. For example, one bit may be set to a logical one to designate a short guard interval or set to a logical zero to designate a long guard interval and the second bit may designate short guard interval length ambiguity mitigation.

The cyclic redundancy check (CRC)1120sequence parameter may comprise a six bit hash of 11ah-SIG1068for error checking and the tail1122parameter may comprise a six bit sequence of, e.g., logical zeros or ones, to designate the end of the signal field, 11ah-SIG1068.

FIG.1Dillustrates an embodiment1200of an operation of one of the functions of a frame. In particular,FIG.1Dillustrates the use on a protected transmission operation (TxOP) for embodiments. Some embodiments may utilize the protected TxOP to inform devices other than the receiver prior to transmission of the frame that the other devices should refrain from transmitting for a particular duration of time. The particular duration of time may be time allocated for transmitting the frame. For instance, for embodiments that utilize Transmit beamforming (TxBF), beamforming may begin with the transmission of the signal field such as the signal field1068illustrated inFIG.1Cor the signal fields1015or1035inFIG.1. As a result, some communications devices such as communications devices1010,1030,1050, and1055may not be able to decode the signal field. In such embodiments, a virtual carrier sensing mechanism may be implemented the to instruct the communications devices to defer from accessing the communications medium such a network1005ofFIG.1for a period of time.

As illustrated inFIG.1D, to establish communications, a transmitter transmits a control frame comprising a Request To Send (RTS) field that is received by a receiver. The control frame also comprises an address field and a duration field (not shown inFIG.1D). The address field indicates to which receiver the transmission is intended. The duration field comprises a Network Allocation Vector (NAV) that indicates the duration of time reserved for the transmission. After the RTS signal is sent, but before the data of the transmission is sent, the transmitter waits to receive a Clear To Send (CTS) signal from the receiver. If the CTS is not received within a short period of time, the intended transmission is temporarily abandoned and a new RTS signal may be sent later. Once the CTS signal is received in response to the RTS, the transmitter sends the data during the duration of the NAV, as shown inFIG.1D. Devices other than the intended receiver may set their respective NAVs to refrain from communications throughout the duration of the NAV.

FIG.2illustrates an embodiment of an apparatus to transmit an orthogonal frequency division multiplexing (OFDM)-based communication in a wireless network. The apparatus comprises a transceiver200coupled with medium access control (MAC) sublayer logic201and a physical layer (PHY) logic250. The MAC sublayer logic201and PHY layer logic250may generate a physical layer protocol data unit (PPDU) to transmit via transceiver200.

The MAC sublayer logic201may comprise hardware and/or code to implement data link layer functionality including generation of MAC protocol data units (MPDUs) from MAC service data units (MSDUs) by encapsulating the MSDUs in frames via a frame builder202. For example, a frame builder may generate a frame including a type field that specifies whether the frame is a management, control or data frame and a subtype field to specify the function of the frame. A control frame may include a Ready-To-Send or Clear-To-Send frame. A management frame may comprise a Beacon, Probe Response, Association Response, and Reassociation Response frame type. The duration field that follows the first frame control field specifies the duration of this transmission. As discussed above, the duration field includes the Network Allocation Vector (NAV), which can be used as a protection mechanism for communications. And the data type frame is designed to transmit data. An address field may follow the duration field, specifying the address of the intended receiver or receivers for the transmission.

The PHY logic250may comprise a data unit builder203. The data unit builder203may determine a preamble based upon a preamble structure such as the preamble structure illustrated inFIG.1Cto encapsulate the MPDU to generate a PPDU. In many embodiments, the data unit builder203may select a preamble from memory such as a default preamble for data frame transmissions, control frame transmissions, or management transmissions. In several embodiments, the data unit builder203may create the preamble based upon a default set of values for the preamble received from another communications device. For example, a data collection station compliant with IEEE 802.11ah for a farm may periodically receive data from low power sensors that have integrated wireless communications devices compliant with IEEE 802.11ah. The sensors may enter a low power mode for a period of time, wake to collect data periodically, and communicate with the data collection station periodically to transmit the data collected by the sensor. In some embodiments, the sensor may proactively initiate communications with the data collection station, transmit data indicative of a communications capability, and begin communicating the data to the data collection station in response to a CTS or the like. In other embodiments, the sensor may transmit data to the data collection station in response to initiation of communications by the data collection station.

The data unit builder203may generate the preamble including an STF, a guard interval, an LTF, and an 11ah-SIG field. In many embodiments, the data unit builder203may create the preamble based upon communications parameters chosen through interaction with another communications device. The data unit builder203may create the preamble with the 11ah-SIG field comprising an MCS field having six bits indicative of Binary Phase-Shift Keying with a coding rate of 1 and four spatial streams. The data unit builder203may determine a bandwidth from five allowed bandwidths such as 16 MHz, 8 MHz, 4 MHz, 2 MHz, and 1 MHz. In further embodiments wherein the bandwidths fall within 1 MHz to 10 MHz, four of the bandwidths may comprise sets of bandwidths such as 10 MHz, 6.7 MHz, 5 MHz, and 4 MHz; 10 MHz, 5 MHz, 4 MHz, and 2.5 MHz; 10 MHz, 5 MHz, 2.5 MHz, and 1.25 MHz; 5 MHz, 4 MHz, 3.3 MHz and 2.9 MHz, or the like. In other embodiments, sets of four bandwidths may comprise one or more bandwidths that are greater than 10 MHz such as 20 MHz, 10 MHz, 5 MHz, and 2.5 MHz; 40 MHz, 20 MHz, 10 MHz, and 5 MHz; 40 MHz, 20 MHz, 10 MHz, and 5 MHz; 26.7 MHz, 20 MHz, 16 MHz, and 13.3 MHz; or the like. The data unit builder203may set the BW bits to values representative of one of the four bandwidths of 10 MHz, 5 MHz, 2.5 MHz, and 1.25 MHz. And in many embodiments, a fifth bandwidth may be selected by another means within the 11ah-SIG field such as a bandwidth parameter with a third bit, an extended data payload with one or more bits that indicate the fifth bandwidth, a setting of another bit within the 11ah-SIG field in conjunction with an indication of the bandwidth parameter being set to a particular bandwidth, or the like.

In many embodiments, the data unit builder203may create the preamble with the 11ah-SIG field comprising a length field that is 16 bits long with the least significant bit (LSB) first. The length field may comprise the length of the transmit vector (TXVECTOR). In further embodiments, the data unit builder203may create a preamble with the 11ah-SIG field comprising a coding bit to select low density parity check (LDPC) and an extra coding bit to offer LDPC duration ambiguity. The data unit builder203may create the preamble with the 11ah-SIG field comprising a bit for transmit beamforming (TxBF). For example, some embodiments may set the TxBF bit to a logical one to indicate that the transmission should be beamformed for data packets to communications devices that have beamforming capabilities and may set the TxBF bit to a logical zero to indicate that the transmission should not be beamformed for, e.g., protection mechanism frames.

In several embodiments, the data unit builder203may create the preamble with the 11ah-SIG field comprising a short guard interval (SGI) field, which may be, e.g., 1.6 microseconds (s) times N, wherein N is the integer by which the timing is down-clocked from 20 MHz channel spacing. The data unit builder203may also create the preamble with the 11ah-SIG field comprising a cyclic redundancy check (CRC) field for error correction and a tail comprising, e.g., six zero bits to enable decoding of, e.g., the MCS and length fields immediately after the reception of the tail bits.

In some embodiments, the data unit builder203may allocate tones for the preamble based upon IEEE 802.11n/ac tone allocations. For example, 56 tones may be allocated for the preamble for the 1.25 MHz bandwidth, 112 tones may be allocated for the 2.5 MHz bandwidth, 224 tones may be allocated for the 5 MHz bandwidth, and 448 tones may be allocated for the 10 MHz bandwidth. In many embodiments, the data unit builder203may allocate tones differently for the data or MPDU portion of the PPDU. For instance, 56 tones may be allocated for the data at the 1.25 MHz bandwidth, 114 tones may be allocated for the data at the 2.5 MHz bandwidth, 242 tones may be allocated for the data at the 5 MHz bandwidth, and 484 tones may be allocated for the data at the 10 MHz bandwidth.

The transceiver200comprises a receiver204and a transmitter206. The transmitter206may comprise one or more of an encoder208, a modulator210, an OFDM212, and a DBF214. The encoder208of transmitter206receives data destined for transmission from the MAC sublayer logic202. The MAC sublayer logic202may present data to transceiver200in blocks or symbols such as bytes of data. The encoder208may encode the data using any one of a number of algorithms now known or to be developed. Encoding may be done to achieve one or more of a plurality of different purposes. For example, coding may be performed to decrease the average number of bits that must be sent to transfer each symbol of information to be transmitted. Coding may be performed to decrease a probability of error in symbol detection at the receiver. Thus, an encoder may introduce redundancy to the data stream. Adding redundancy increases the channel bandwidth required to transmit the information, but results in less error, and enables the signal to be transmitted at lower power. Encoding may also comprise encryption for security.

In the present embodiment, the encoder208may implement a binary convolutional coding (BCC) or a low density parity check coding (LDPC), as well as other encodings.

The modulator210of transmitter206receives data from encoder208. A purpose of modulator210is to transform each block of binary data received from encoder208into a unique continuous-time waveform that can be transmitted by an antenna upon up-conversion and amplification. The modulator210impresses the received data blocks onto a sinusoid of a selected frequency. More specifically, the modulator210maps the data blocks into a corresponding set of discrete amplitudes of the sinusoid, or a set of discrete phases of the sinusoid, or a set of discrete frequency shifts relative to the frequency of the sinusoid. The output of modulator210is a band pass signal.

In one embodiment, the modulator210may implement Quadrature Amplitude Modulation (QAM) impressing two separate k-bit symbols from the information sequence onto two quadrature carriers, cos (2πft) and sin(2πft). QAM conveys two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme. The two carrier waves are out of phase with each other by 90° and are thus called quadrature carriers or quadrature components. The modulated waves are summed, and the resulting waveform is a combination of both phase-shift keying (PSK) and amplitude-shift keying (ASK). A finite number of at least two phases and at least two amplitudes may be used.

In another embodiment, the modulator210maps the blocks of data received from encoder208into a set of discrete phases of the carrier to produce a Phase-Shift Keyed (PSK) signal. An N-phase PSK signal is generated by mapping blocks of k=log2N binary digits of an input sequence into one of N corresponding phases θ=2π(n−1) n for n a positive integer less than or equal to N. A resulting equivalent low pass signal may be represented as

u⁡(t)=∑n=0∞ej⁢θn⁢g⁡(t-n⁢T)
where g(t-nT) is a basic pulse whose shape may be optimized to increase the probability of accurate detection at a receiver by, for example, reducing inter-symbol interference. Such embodiments may use Binary Phase-Shift Keying (BPSK), the simplest form of phase-shift keying (PSK). BPSK uses two phases which are separated by 180° and is the most robust of all the PSKs since it takes the highest level of noise or distortion to make the demodulator reach an incorrect decision. In BPSK, there are two states for the signal phase: 0 and 180 degrees. The data is often differentially encoded prior to modulation.

In yet another embodiment, the modulator210maps the blocks of data received from encoder208alternately on two channels or streams called the I channel (for “in phase”) and the Q channel (“phase quadrature”), which is referred to as staggered quadrature phase-shift keying (SQPSK). SQPSK is a method of phase-shift keying in which the signal carrier-wave phase transition is 90 degrees or ¼ cycle at a time. A phase shift of 90 degrees is known as phase quadrature. A single-phase transition does not exceed 90 degrees. In SQPSK, there are four states: 0, +90, −90 and 180 degrees.

The output of modulator210may be up-converted to a higher carrying frequency. Or, modulation may be performed integrally with up-conversion. Shifting the signal to a much higher frequency before transmission enables use of an antenna array of practical dimensions. That is, the higher the transmission frequency, the smaller the antenna can be. Thus, an up-converter multiplies the modulated waveform by a sinusoid to obtain a signal with a carrier frequency that is the sum of the central frequency of the waveform and the frequency of the sinusoid. The operation is based on the trigonometric identity:

sin⁢A⁢cos⁢B=12[sin⁡(A+B)+sin⁡(A-B)]
The signal at the sum frequency (A+B) is passed and the signal at the difference frequency (A−B) is filtered out. Thus, a band pass filter is provided to ideally filter out all but the information to be transmitted, centered at the carrier (sum) frequency.

The output of modulator210may be fed to an orthogonal frequency division multiplexer (OFDM)212via a space-time block coding (STBC). OFDM212impresses the modulated data from modulator210onto a plurality of orthogonal sub-carriers. The output of the OFDM212is fed to the digital beam former (DBF)214. Digital beam forming techniques are employed to increase the efficiency and capacity of a wireless system. Generally, digital beam forming uses digital signal processing algorithms that operate on the signals received by, and transmitted from, an array of antenna elements to achieve enhanced system performance. For example, a plurality of spatial channels may be formed and each spatial channel may be steered independently to maximize the signal power transmitted to and received from each of a plurality of user terminals. Further, digital beam forming may be applied to minimize multi-path fading and to reject co-channel interference.

The transceiver200may also comprise diplexers216connected to antenna array218. Thus, in this embodiment, a single antenna array is used for both transmission and reception. When transmitting, the signal passes through diplexers216and drives the antenna with the up-converted information-bearing signal, x. During transmission, the diplexers216prevent the signals to be transmitted from entering receiver204. When receiving, information bearing signals received by the antenna array pass through diplexers216to deliver the signal from the antenna array to receiver204. The diplexers216then prevent the received signals from entering transmitter206. Thus, diplexers216operate as switches to alternately connect the antenna array elements to the receiver204and the transmitter206.

Antenna array218radiates the information bearing signals into a time-varying, spatial distribution of electromagnetic energy that can be received by an antenna of a receiver. The receiver can then extract the information of the received signal. An array of antenna elements can produce multiple spatial channels that can be steered to optimize system performance. Reciprocally, multiple spatial channels in the radiation pattern at a receive antenna can be separated into different spatial channels. Thus, a radiation pattern of antenna array218may be highly selective. The antenna array218may be implemented using printed circuit board metallization technology. Microstrips, striplines, slotlines, and patches, for example, are all candidates for the antenna array218.

The transceiver200may comprise a receiver204for receiving, demodulating, and decoding information bearing signals. The receiver204may comprise one or more of a DBF220, an OFDM222, a demodulator224and a decoder226. The received signals are fed from antenna elements218to a DBF220. The DBF220transforms N antenna signals into L information signals.

The output of the DBF220is fed to the OFDM222. The OFDM222extracts signal information from the plurality of subcarriers onto which information-bearing signals are modulated.

The demodulator224demodulates the received signal. Demodulation is the process of extracting information from the received signal to produce an un-demodulated information signal. The method of demodulation depends on the method by which the information is modulated onto the received carrier signal. Thus, for example, if the modulation is BPSK, demodulation involves phase detection to convert phase information to a binary sequence. Demodulation provides to the decoder a sequence of bits of information. The decoder226decodes the received data from the demodulator224and transmits the decoded information, the MPDU, to the MAC sublayer logic202.

Persons of skill in the art will recognize that a transceiver may comprise numerous additional functions not shown inFIG.2and that the receiver204and transmitter206can be distinct devices rather than being packaged as one transceiver. For instance, embodiments of a transceiver may comprise a dynamic random access memory (DRAM), a reference oscillator, filtering circuitry, synchronization circuitry, possibly multiple frequency conversion stages and multiple amplification stages, etc. Further, some of the functions shown inFIG.2may be integrated. For example, digital beam forming may be integrated with orthogonal frequency division multiplexing.

FIG.3depicts an example flowchart300for generating a preamble structure such as the preamble structures illustrated inFIGS.1A and1B. The flowchart300begins with receiving a frame from the frame builder (element305). The MAC sublayer logic may generate a frame to transmit to another communications device and may pass the frame as an MPDU to a data unit builder that transforms the data into a packet that can be transmitted to the other communications device. The data unit builder may generate a preamble based upon a preamble structure, like the preamble structure1062inFIG.1A, to encapsulate the PSDU (the MPDU from the frame builder) to form a PPDU for transmission. In some embodiments, more than one MPDU may be encapsulated in a PPDU.

The data unit builder may determine or create a preamble to encapsulate the frame with one or more of the elements310through345. In generating the preamble, the data unit builder may generate a signal field such as 11ah-SIG1068inFIGS.1A-Calthough the fields and their content may differ from the fields described with respect toFIG.1C. To generate the signal field, the data unit builder may determine a modulation and coding scheme for the PPDU (element310). The data builder may select a default modulation and coding scheme, select a modulation and coding scheme indicated via communications with the other communications device, or otherwise select a modulation and coding scheme. In many embodiments, the data unit builder may select a modulation and coding scheme from a group of modulation and coding schemes comprising BPSK at a rate of ½, 256-QAM at a rate of ¾, or SQPSK.

While the generation of fields of the preamble may occur in any order or may comprise selection of a preamble from memory, the present embodiment may determine the bandwidth of the communication (element315) after determining the modulation and coding scheme. Determining the bandwidth may comprise selecting a bandwidth from five bandwidths such as 1 MHz, 2 MHz, 4 MHz, 8 MHz and 16 MHz.

The data unit builder may determine if beamforming should be implemented by setting the beamforming bit (element320). The data unit builder may set the beamforming bit to a logical one to implement beamforming for data frames and may set the beamforming bit to a logical zero to turn off beamforming for a number of different reasons. For instance, beamforming may be turned off when the communications device originating the transmission or the communications device to which the transmission is addressed does not support beamforming.

In many embodiments, the data unit builder determines the space-time block coding (STBC) bit (element325) by setting the bit to a logical one turn on STBC and to a logical zero to turn off STBC. STBC may transmit multiple copies of a data stream across a number of antennas and to exploit the various received copies of the data to improve the reliability of data-transfer. This redundancy results in a higher chance of being able to use one or more of the received copies to correctly decode the received signal. In several embodiments, STBC combines all the copies of the received signal to extract as information from each of the copies.

After determining the STBC value, the data unit builder may determine the coding value (element330). The data unit builder may determine whether to use binary convolutional coding (BCC) or low density parity check coding (LDPC). In some embodiments, the coding parameter may include an extra bit for LDPC duration ambiguity. The BCC may be viewed as a linear finite-state shift register with an output sequence comprising a set of linear combinations of the input sequence. The number of output bits from the shift register for each input bit may be a measure of the redundancy in the code. And the LDPC code is a linear error correcting code, a method of transmitting a message over a noisy transmission channel, and may be constructed using a sparse bipartite graph. LDPC codes are capacity-approaching codes, which can be decoded in time linear to their block length and are defined by a sparse parity-check matrix.

In some embodiments, the data unit builder may determine the aggregation value by setting the aggregation value to a logical one to mandate an aggregated MPDU (A-MPDU) (element335). In mandating an aggregated MPDU, the data unit builder may require that each data transmission of a PPDU include more that one MPDU in the data payload. Because management information needs to be specified only once per PPDU, the ratio of payload data to the total volume of data transmitted is higher, allowing lower power consumption.

The data unit builder may then determine the short guard interval (SGI) value (element340). In many embodiments, the data unit builder may select between two or more SGI values. For example, the data unit builder may set the SGI value to a logical zero to select an SGI of 400 nanoseconds and set the SGI value to a logical one to select an SGI of 600 nanoseconds.

In several embodiments, the data builder may complete the preamble with a cyclic redundancy check (CRC) (element345) and a tail. The CRC may include, e.g., a type of hash function used to produce a checksum in order to detect errors in data transmission and the tail may comprise a series of bits such as six logical zeros to designate the end of the preamble.

After determining the preamble, the data unit builder may encapsulate the frame (MPDU), or multiple frames if A-MPDU is set to a logical one, with the preamble to generate a PPDU for transmission to another communications device (element350). The PPDU may then be transmitted to the physical layer device such as the transmitter206inFIG.2or the transceiver1020,1040inFIG.1so the PPDU may be converted to a signal based upon the preamble and transmitted via an antenna (element355). If more frames are received (element360) from the frame builder then additional PPDUs may be determined in elements310through350.

FIGS.4A-Bdepict embodiments of flowcharts to transmit and receive communications with a transmitter and a receiver as illustrated inFIG.2. Referring toFIG.4A, the flowchart400begins with a transmitter such as transmitter206receiving a PPDU from MAC sublayer logic via PHY logic (element405). The transmitter may convert the PPDU to a communication signal (element410) that can be transmitted via an antenna such as an antenna element of antenna array218. More specifically, the transmitter may encode the PPDU via one or more encoding schemes described in a preamble of the PPDU such as BCC or LDPC. The transmitter may modulate the PPDU via a modulation and coding scheme indicated by the preamble such as BPSK, 16-QAM, 64-QAM, 256-QAM, QPSK, or SQPSK. The transmitter may divide the data amongst the subcarriers via OFDM in accordance with the preamble and the transmitter may beamform signals to create a communication signal. Thereafter, the transmitter may transmit the communication signal to the antenna(s) to transmit the signal to another communications device (element415).

Referring toFIG.4B, the flowchart450begins with a receiver such as the receiver204receiving a communication signal via one or more antenna(s) such as an antenna element of antenna array218(element455). The receiver may convert the communication signal to a MPDU in accordance with the process described in the preamble (element460) such as a preamble based upon the preamble structure1062or1082inFIGS.1A-B. More specifically, the received signal is fed from the one or more antennas to a DBF such as the DBF220illustrated inFIG.2. The DBF transforms the antenna signals into information signals such as illustrated inFIG.3B. The output of the DBF is fed to OFDM such as the OFDM222. The OFDM extracts signal information from the plurality of subcarriers onto which information-bearing signals are modulated. Then, the demodulator such as the demodulator224demodulates the signal information via, e.g., BPSK, 256-QAM, or SQPSK. And the decoder such as the decoder226decodes the signal information from the demodulator via, e.g., BCC or LDPC, to extract the MPDU (element460) and transmits the MPDU to MAC sublayer logic such as MAC sublayer logic202(element465).

Another embodiment is implemented as a program product for implementing systems and methods described with reference toFIGS.1-4. Some embodiments can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment containing both hardware and software elements. One embodiment is implemented in software, which includes but is not limited to firmware, resident software, microcode, etc.

Furthermore, embodiments can take the form of a computer program product (or machine-accessible product) accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device). Examples of a computer-readable medium include a semiconductor or solid-state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W), and DVD.

A data processing system suitable for storing and/or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.

The logic as described above may be part of the design for an integrated circuit chip. The chip design is created in a graphical computer programming language, and stored in a computer storage medium (such as a disk, tape, physical hard drive, or virtual hard drive such as in a storage access network). If the designer does not fabricate chips or the photolithographic masks used to fabricate chips, the designer transmits the resulting design by physical means (e.g., by providing a copy of the storage medium storing the design) or electronically (e.g., through the Internet) to such entities, directly or indirectly. The stored design is then converted into the appropriate format (e.g., GDSII) for the fabrication.

The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product.