Robust preamble generation techniques for scalable packets in long-distance wireless networks

Abstract

Robust preamble generation techniques for scalable packets in long-range wireless networks are provided. In one aspect, a circuit includes a preamble generator to generate a preamble having a first field and a second field, the first field having a first sequence repeated a number of times, a length of the first sequence and a number of times based at least in part on a distance between a transmitter and a receiver.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is a continuation-in-part of U.S. patent application No. 18 / 342,975 filed on June 28, 2023, the contents of which are hereby incorporated by reference. Background Art

[0003] In long-range wireless systems, especially when utilizing low-power "random access" transceivers (which do not always have to be perfectly synchronized, nor do they have to consider time slot access standards), the way information packets are exchanged is critical and requires well-designed signal preambles. These preambles allow the intended receiver to initiate the detection verification and synchronization process to further demodulate and decode the packet information - if it is targeted at that receiver (with sufficient reliability) (and preferably only in this case). Several trade-offs must be considered, especially to be robust in unlicensed bands while complying with relevant regulations and maximum "energy density" constraints. Many current systems are not scalable appropriately and are implemented with compromise or worst-case design settings, which increases complexity and power consumption, and wastes resources. As a result, these trade-offs reduce the performance of global wireless networks in real environments. Summary of the invention

[0004] In one aspect, an apparatus includes: a circuit for generating a packet having at least one of a header or a data portion and a preamble, wherein the preamble includes a first field and a second field, the first field including a first sequence repeated a plurality of times, a length of the first sequence and the number of times being based at least in part on a distance between the apparatus and a receiver; and a radio frequency (RF) front end circuit coupled to the circuit for processing and transmitting the packet.

[0005] In one implementation, the apparatus further includes a controller coupled to the circuit, wherein the controller determines parameters of the preamble based at least in part on the distance parameter and the group parameter, the parameters including a length of the first sequence and a number of times to identify a network having the apparatus and the receiver.

[0006] In one implementation, the controller is configured to pre-negotiate at least a first sequence with a receiver. The circuit is configured to generate a preamble having the first sequence, the first sequence having a full ramp over the bandwidth of the preamble, so that continuity of phase and discrete time-frequency blocks can be achieved once sampled at a given bandwidth frequency at the receiver, the receiver including an unsynchronized receiver to perform correlation between the first field and an expected sequence corresponding to the first sequence.

[0007] In one implementation, the circuit is used to generate a preamble having a second field, the second field including a second sequence repeated a second number of times. The circuit is used to perform at least one operation according to an operation scheme on the second sequence for some of the second number of times. The circuit is used to perform at least one operation according to an operation scheme on the second sequence for some of the second number of times, the operation scheme including one or more of the following: a phase shift operation; a frequency shift; a conjugate operation; a time reversal; or a ramp operation. The circuit is used to generate a first sequence having a value and a bandwidth based at least in part on a distance and a sub-portion of a group parameter, the group parameter sub-portion identifying at least one of a network or service having the device and the receiver to enable packet detection and mitigate interference and reduce false alarms.

[0008] In one implementation, the circuit is used to generate a preamble including a third field having a third sequence repeated a third plurality of times, the circuit is used to perform at least one operation according to an operation scheme on the third sequence for at least some of the third plurality of times, wherein the third sequence is used to implement further packet validation, enable non-intended receivers to filter the packet, and implement synchronization to retrieve time and frequency accurate estimates and alignment with a transmitter.

[0009] In one implementation, the apparatus further comprises at least one memory for storing a table, the table comprising a plurality of sequences from which the first sequence is to be selected. The circuit may generate a preamble having a first bandwidth that is smaller than a bandwidth of the header and the data portion.

[0010] In another aspect, a method includes determining, in a controller of a transmitter, a first sequence and a second sequence of preambles of a packet based at least in part on a distance between the transmitter and a receiver and a group identifier known at the transmitter and the receiver in a network including the transmitter and the receiver; forming a first portion of the preamble including first multiple repetitions of the first sequence; forming a second portion of the preamble including second multiple repetitions of the second sequence, including performing a plurality of operations according to an operation scheme on one or more of the second multiple repetitions of the second sequence; and transmitting, from the transmitter, an RF signal including the packet, the packet including the preamble.

[0011] In one implementation, the method further includes: when the distance is less than a first distance, forming a first part of a preamble code including a first number of first multiple repetitions, the first sequence having a first length; and when the distance exceeds the first distance, forming a first part of a preamble code, the first part including at least one of: a second number of first multiple repetitions, the second number being greater than the first number; and a first sequence having a second length greater than the first length.

[0012] In one implementation, the method further includes: forming a first portion of a preamble code comprising first multiple repetitions of a first sequence, each of the first multiple repetitions having a first slope; and forming a second portion of a preamble code comprising second multiple repetitions of a second sequence, each of the second multiple repetitions having a second slope, the second slope being different from the first slope.

[0013] In another aspect, a system includes a transceiver, the transceiver including: a preamble generator for generating a preamble for a packet including a preamble, a header, and a data portion, the preamble including: a first field including a first sequence repeated a first plurality of times, wherein: a first length of the first sequence and the number of the first plurality of times are based on a distance parameter associated with a distance capability between a system and a receiver; and the first sequence includes a first ramp and a first bandwidth that depend at least in part on a group parameter of a network including the system and the receiver; and a second field including a second sequence repeated a second plurality of times to provide phase continuity, wherein: the second sequence includes a second ramp, the preamble generator applies an operating scheme to at least some of the second plurality of times of the second sequence, the operating scheme depending at least in part on the group parameter. The transceiver also includes an RF front-end circuit for forming an RF signal including the preamble, the header, and the data portion, the RF front-end circuit for transmitting the RF signal. The system also includes a non-volatile memory that stores at least the first sequence.

[0014] In one implementation, a preamble generator is used to generate: a first field comprising a first sequence, the first sequence comprising a first linear scan repeated a first plurality of times; and a second field comprising a second sequence, the second sequence comprising a second linear scan repeated a second plurality of times to provide phase and frequency continuity.

[0015] In another implementation, a preamble generator is used to generate: a first field comprising a first sequence, the first sequence comprising a first linear scan repeated a first plurality of times, the preamble generator applying a first operation scheme to at least some of the first plurality of times of the first sequence to provide phase and frequency continuity; and a second field comprising a second sequence, the second sequence comprising a second linear scan repeated a second plurality of times to provide phase and frequency continuity, wherein at least the second field is used to achieve multi-user and interference scaling and mitigation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a block diagram of a transmitter according to an embodiment.

[0017] Figure 2A is a graphical illustration of grouping according to an embodiment.

[0018] Figure 2B is an example of a preamble code using a first distance of an embodiment.

[0019] Figure 2C is an example of a preamble code using the second distance of an embodiment.

[0020] Figure 2D-2E is an example of a preamble using another embodiment.

[0021] Figure 3 is a block diagram of a more detailed implementation of a transmitter according to an embodiment.

[0022] Figure 4 is a block diagram of a receiver according to an embodiment. DETAILED DESCRIPTION

[0023] In various embodiments, a preamble framework for a wireless system is provided, which has an elegant solution that is scalable enough to meet most of the needs of today's long-distance networks. The preamble according to the embodiment is efficient (e.g., lowest power, shortest packet), robust and low-cost (in the presence of impairments and interference, a fairly simple receiver processing about robustness is achieved). In an embodiment, available resources can be used carefully, with limited and good energy spread in the bandwidth and duration allocated to network users. In one or more implementations, for efficient, low-cost, low-power transceivers, packets have reasonable bandwidth and limited power changes over time, i.e., low peak-to-average power ratio (PAPR), and provide easy detection / synchronization / demodulation solutions, even in the case of low signal-to-interference-plus-noise ratio (SINR) for a variety of scenarios. For an embodiment, reduced duration and delay can also contribute to network management and efficiency. The optimization and balancing of the preamble as described herein can be targeted at efficient, low-power long distances and reduce resource usage / pollution for next-generation scalable standards.

[0024] In various embodiments, preamble generation as described herein may be performed by a transmitter configured to transmit a signal and modulate information for a long-distance scenario. Although embodiments are not limited in this regard, as an example, the transmitter may be configured to dynamically control modulation aspects to enable transmission of wireless signals over relatively long distances (e.g., up to approximately tens or hundreds of kilometers).

[0025] Embodiments herein pay special attention to this dynamic control of the preamble of packet communication.This preamble is independent of modulation scheme.And further note that the constraint to waveform may be different for header and data than for preamble.However, first describe the example modulation scheme for header and / or data part, to set the example context of preamble formatting described herein.It should be understood that this preamble formatting can be used for the grouping with many different types of modulation schemes for header and data part.

[0026] In an embodiment, a constant amplitude, and in particular a constant amplitude zero autocorrelation (CAZAC) sequence may be used as a signal element to be transmitted. Typically, a CAZAC sequence is a polyphase sequence having a periodic complex valued signal with a modulus of one and an out-of-phase periodic (cyclic) autocorrelation equal to zero. In an embodiment, an example of constructing such a signal sequence may be a combination of a selected quasi-CAZAC sequence and an orthogonal frequency division multiplexing (OFDM) principle. The selected CAZAC sequence may be close to a Zadoff-Chu (ZC) sequence, or a more generalized linear frequency modulation sequence (GCS). Such a GCS precoded or ZC precoded OFDM signal may be used as the basis for defining a modulation scheme that is robust to long-distance scenarios. These sequences may optionally be transformed into another domain, for example, using a Fourier transform (discrete Fourier transform (DFT) or fast Fourier transform (FFT) processing) of an OFDM system, with potential further signal processing to shape the signal (e.g., windowing, filtering, power compression) to provide the desired properties. Such a sequence is referred to herein as a scanning sequence (SS), or more generally a "sequence", and may be formed of tens to thousands of complex-valued samples.

[0027] The length is N zc A generalized linear frequency modulation sequence (GCS) of complex samples with parameters (P, Q, U, S) can be defined by the following equation:

[0028]

[0029] Where P, Q, U, and S do not need to be integers.

[0030] As a subset, the length of the potential cyclic shift q is N zc The root Zadoff-Chu sequence of complex samples of and root u is defined by the following equation:

[0031] S zc(Nzc，u) [n]=exp(-j.π.n.(u(n+c)+2q) / N zc ), 0≤n<N zc ,

[0032] Among them, for even number N zc , c is usually 0, and for the default odd N zc , c is usually 1 (if repeated, to ensure cyclicity / continuity); u is an integer identifying the ZC sequence, called the root index. ZC is a special case of GCS, where S = 0, P = 0, and the integer u = -U. When N zc When N is an even number, q = -Q / 2, and when N zc When it is an odd number, q=-(Q / 2+U / 2).

[0033] These ZCs are polyphase sequences with perfect periodic autocorrelation functions (i.e., complex sequences with unit amplitude and null autocorrelation for all cyclic shifts except zero). However, it is considered that a compromise of a pool of sequences with low shift autocorrelation and low cross-correlation may be sufficient for a given application on subsequent parts of the packet.

[0034] N f The OFDM(I)DFT transformation of complex samples is based on the following equation:

[0035]

[0036] The DFT (or FFT) processing ensures signal continuity at the sequence edges and also allows resampling (the final SS bandwidth may be different from the initial / sampling bandwidth, filling the edge FFT bins with zeros, e.g. when Nf>Nzc).

[0037] ZC-OFDM is a combination of these two processing functions, with potential intermediate and / or post-processing to shape the signal (e.g., centering, filtering, windowing, shifting, power compression). zc , N fft =N f .L) and the sampling rate (which also defines the SS bandwidth and duration), there are several conceivable quasi-orthogonal sequences (up to Nzc for ZC-OFDM with integer u). Note that the sequences can be oversampled by a factor of L to further improve the signal shaping and properties (e.g., using a length of N). fft =N f L instead of N fft =N f ≥N zc higher FFTs, finer tuning / filtering and management of PAPR / out-of-band (OoB).

[0038] As another subset of GCS where U=0 and S=0, ultra-narrowband simple carrier (constant frequency per block) sequences or frequency-hopping single carrier sequences also have low PAPR and are, for example, [0, ..N zc ] are special cases that provide some capabilities of several orthogonal sequences (or semi-orthogonal once different coding / hopping and / or operating schemes are applied to each user). For a given SS, the segmented non-scanned ultra-narrowband sequence may appear less robust than the presented CAZAC sequence with respect to certain noise and interference, but the robustness and good use of the allocated spectrum can be recovered from the scheme described later in this document. Then, designing the sequence list by hopping subcarriers (segmented pure sine waves) is also a low-rate solution for sharing scarce resources and is equivalent to precoded-OFDM, where the size is N fftThe precoding vector of is all zero except for one element at a time (1 complex value on the unit circle). However, a general receiver in this case may need different algorithms with potentially higher complexity to demodulate or synchronize (especially in real multipath or fast fading channels with spurs), just like the less ideal spectrum (and potential dependence on filtering processes) compared to ZC and ZC-OFDM sequences. Moreover, depending on the averaging period considered for calculating the spectrum, a more "spike in frequency" solution may be more limited in power by regulations for accessing some wireless channels / bands.

[0039] As another intermediate example list of sequences, a subset of GCs with low scan slopes (non-integer 0 <|U| <1 and / or more zeros on the edges in the subsequent OFDM FFT) and S = 0 can provide a scan sequence with low PAPR and the ability to provide several orthogonal sequences (or weakly correlated) with another trade-off in robustness to interference in time / frequency, the number of simultaneous packets on the same frequency band, and group management. The associated spectrum of each SS does not spread the energy equally like the GCS / ZC-based sequences with integer U ≥ 1, but the scheme description in the next processing stage will allow further appropriate spreading of the signal over the system bandwidth while still allowing simplified receiver processing of the scan sequence in a real channel (with multipath interference). With weighted aggregation of such blocks from modulation, a simple receiver robust to any noise (including localized interferers "frequency spikes" and "time spikes") is possible. Then, based on the equations and solutions presented, users in the art can easily adjust the parameters and durations to meet requirements and regulations. This low ramp high localized power can be used in the second part of the preamble to verify the packet signature in several solutions and define a specific but well-designed signal (e.g., continuous, well-shaped in time and frequency, with very low PAPR and limited bandwidth), and also allows efficient and accurate synchronization refinement of the preamble.

[0040] In one or more embodiments, the transmitter may generate and / or store such a pool of sequences. These sequences may be optimized specifically for long-range wireless communications, with specific properties including the following. As described above, the sequences may achieve good shaping in time and frequency that is better than general (worst case) OFDM, with low power variation over time (low PAPR), and good shaping in frequency (ideal spectrum for the application, with low out-of-band emissions). These sequences may also have good autocorrelation and cross-correlation coefficients, such as localized cyclic autocorrelation (almost empty except for zero shift autocorrelation).

[0041] In general, for the preamble portion, the sequence provides a way to easily detect the packet signature (primarily defined by the slope and bandwidth in the first part of the preamble) and synchronize the receiver in time and frequency. In one or more embodiments, the preamble waveform can be configured to be well-shaped (low power variation, i.e., PAPR close to 0dB, and low OoB emissions, i.e., good spectrum mask) and allow the receiver to easily detect and synchronize. To this end, an embodiment provides a preamble that avoids discontinuities at the edges of blocks when connecting sequences and has a selected variation (phase / frequency / slope) on the preamble.

[0042] Note that, if desired, scan sequences with different slopes can provide reasonable differentiation (as long as the slopes are separated enough, e.g., >5% difference in blocks of about 100 samples) to allow packet detection / identification, among other things, to increase multiple access capabilities in large networks.

[0043] Several properties like symmetry / repetition can exist between sequences (for example, when a sequence is antisymmetric, the conjugation of the sequence is usually its reversed version, usually representing a frequency sweep in the other direction, and u' = N zc -u), and can also save memory. These sequences are usually close to frequency scanning sequences (CSS can be regarded as a special case of ZC-OFDM, where the whole N zc =N fft The simplest scan is with u=1 and no windowing), i.e., one or several tone scans (less than once, once, or a few times) can be approximated over the allocated area (given bandwidth and sequence duration).

[0044] Using this SS as a basis, symbol modulation and spreading (SME) can be generated to efficiently transmit information. SME is a combination of the modulation of the SS and the spreading of the signal repeated (e.g., 4 modulation SSI repetitions). In addition, each of these spread SSs can have one or more operations (from the scheme) performed on it, as further described below.

[0045] Note that in one embodiment, the same SS is used for repetitions in a given SME (even though potentially different operations are performed on the SS for each repetition within the SME). In an embodiment, for simplicity, a limited set of operations within the SME may be used. For example, in one implementation, these operations may include: conjugate operators and / or time reversals, i.e., SS'(n) = conj(SS(n)) or SS'(n) = SS(Nn), n = 0, ... N-1; phase operations (e.g., the extended general case of + / -{1, j}), i.e., SS'(n) = exp(j.θ).SS(n); frequency shifts (e.g., from a numerically controlled oscillator (NCO)), i.e., SS'(n) = SS(n)·exp(j.2π.δ.n / N), typically |δ|≤1 if small / fractional frequency shifts are primarily used to improve signal continuity or spectrum usage at the edges, or any larger δ if the frequency shifts are also used to manage interference mitigation; and / or any combination of all of these operations.

[0046] Note that the SME extension is presented as an integer number of SS repetitions to simplify the description, but can also be extended slightly, similar to the OFDM cyclic prefix, to better manage the SME edges in real channels with echoes. As an example, instead of a cyclic extension of 3 times SS, in order to have 4 cyclic repetitions of SS, there can be 4.25 cyclic repetitions of SS (with a quarter symbol to smooth the signal and minimize inter-symbol interference when echoes and filtering are present).

[0047] Note that in embodiments, SS reversal (negative) and π / 2 rotation (j) are special cases of phase operators, and conjugation is generally a special case of time reversal with potential frequency shift (when the sequence describes symmetry, the sequence plays in the other direction).

[0048] Embodiments implementing swept wide area modulation (SWAM) may be viewed as a modulation technique for the entire packet or one or more portions (e.g., the data portion) of a packet. Depending on the implementation, such precoded OFDM modulation may be included as an additional mode or "modulation and coding scheme" (MCS) for Smart Ubiquitous Networks (SUN-OFDM) for wireless, or as a building block for a new and optimized system / standard that is more flexible and a superset of large-scale low-rate networks (such as IEEE 802.15.4g WiSUN).

[0049] Reference now Figure 1 , shows a block diagram of a transmitter according to an embodiment. More specifically, as Figure 1 As shown in , according to an embodiment, the transmitter 100 is configured to transmit packets according to a communication protocol. Figure 1In the view of FIG. 1 , all components (except antenna 150) may be implemented on one or more dies of an integrated circuit (IC). In some cases, all circuits may be implemented on a single semiconductor die, while in other cases, multiple dies may be present within an IC package. Transmitter 100 may be configured to send a preamble, and then utilize each information bit at antenna 150 (for reliability) through a dedicated block, adapted to the selected modulation order and coding scheme.

[0050] As shown, incoming information in the form of an input bit stream (which may be generated within the digital circuitry of the transmitter or a device coupled to the transmitter) is input into a scrambler 110. In various embodiments, the scrambler 110 (which may be optional in some embodiments) may scramble and / or whiten the incoming bits before providing them to a bit-to-symbol encoder (typically encoder 120). Figure 1 In a high-level view of FIG. 1 , encoder 120 is shown having constituent components, including encoder 122, interleaver 124, and mapper 126. Encoder 122 is configured to perform FEC encoding on incoming bits. The encoded bits are in turn provided to an optional interleaver 124, which may interleave the incoming bits according to a given interleaving scheme. The interleaved bits are then provided to mapper 126, which performs optional reordering and bit-to-symbol mapping, thereby outputting corresponding symbols from one or more incoming bits. Note that selected block FEC may perform integrated "smart bits-to-symbol" encoding and mapping (especially for small blocks like headers), thereby eliminating the need for additional interleavers and remappers / reordering.

[0051] Still reference Figure 1 , the symbols are provided to the SWAM modulator 130. As will be described herein, the SWAM modulator 130 can use the SS sequence to perform modulation of the incoming symbols. In addition, the modulation symbols can be spread, where the symbols are repeated, e.g., copied one or more times. Additional processing, a so-called manipulation scheme, can then be performed on each of these symbol copies. Thereafter, optional signal shaping can be performed.

[0052] The resulting sequence of optionally shaped / filtered / smoothed blocks of samples (for a preamble or modulation and spreading symbol (SME)) is provided to a radio frequency (RF) front end circuit 140. Various digital and analog processing, including up-conversion to RF levels, filtering, gain control, and amplification (including in a power amplifier of the RF front end circuit 140), may be performed to produce a transmit RF signal that is transmitted via an antenna 150.

[0053] Still reference Figure 1, there is a controller 160. In various embodiments, the controller 160 is configured to control the components of the transmitter 100. In a particular embodiment, the controller 160 may be a programmable hardware circuit configured to execute instructions such as may be stored in one or more non-transitory storage media.

[0054] In an embodiment, the controller 160 may determine the appropriate SS to use for modulation based at least in part on the input parameters and / or symbol index, and determine the appropriate operation scheme to perform on the SS. Further, the controller 160 may be configured to control any optional signal shaping performed in the SWAM modulator 130.

[0055] Although the above discussion refers to a particular modulation scheme for the header and / or data portion, it should be appreciated that the techniques described herein focusing on the preamble may be used with many other types of modulation schemes.

[0056] Still reference Figure 1 , the transmitter 100 further includes a preamble generator 170. In an embodiment, under the control of the controller 160, the preamble generator 170 is configured to generate a preamble having a plurality of parts, each part being formed by a dynamically determined signal (but generally known in advance by the intended / target receiver), each part having a determined length. In addition, one or more operations (determined as an operation scheme by the controller 160) may be performed on at least a portion of the sequence.

[0057] In an exemplary embodiment, the preamble is formed of at least two parts. The first part (referred to as STF0) is composed of L0 repetitions of a sequence S0, and the second part (referred to as STF1) is composed of L1 repetitions of another sequence S1. The second part can be formed using potential operations for one or more repetitions. These operations can be obtained from an operation pool defined by a scheme vector.

[0058] The controller 160 can cause the preamble generator 170 to generate the preamble with a waveform that is as "good" as possible (in terms of continuity / shaping, because there is no non-deterministic information to be modulated and transmitted). That is, the controller 160 can pre-calculate the deterministic waveform to be expected by the receiver. This control enables low power operation of both the transmitting (TX) and receiving (RX) devices. The TX sends a packet including a preamble, which consumes low power (because it is typically sent at constant power or nearly constant power) as a low complexity signal, and the RX can detect the expected packet preamble in a noisy environment (where there are multiple devices and channel interference in addition to the usual impairments), and properly synchronize and correct mismatches between the TX and RX (e.g., time and frequency errors / offsets). Although in Figure 1The embodiments are shown at this high level, but many variations and alternatives are possible.

[0059] Embodiments enable early identification of packets and interference mitigation, providing advantages in global multi-user systems. Continuing with the above discussion of preambles, all sequences / repetitions have the same block duration (known at both the transmitter and receiver sides), allowing simple block processing with two-stage diversity recovery at the receiver. This block processing at the receiver includes a first recovery operation, such as by length tractable (N) correlation / fast Fourier transform (FFT) and analysis with the expected sequence, and a second recovery operation via intelligent / weighted combination of the analysis results to further increase robustness in harsh channels and environments.

[0060] In some embodiments, at least the end of the second part (STF1) may contain alternative scheme operations that do not change the default basic analysis in the modulus, but can help reduce interference between similar packets, provide additional information to further improve performance, and allow early packet filtering if the packet is not targeted at a specific receiver. This early filtering can be achieved using frequency changes, signal complex conjugation (= scanning in the other direction) and even optional phase operations, once the receiver is sufficiently synchronized.

[0061] In some embodiments, the preamble may include an optional third part (also referred to as "STF2"). This additional preamble field may be based on sequence S2 (which may be equivalent to S0 and / or S1) with a dedicated scheme operator vector to further improve performance and distinguish the packet from other signals and filter / select remaining processing early at the receiver.

[0062] For an embodiment, the transmitter can generate a preamble that simplifies both TX and RX operations, enabling use in low-cost, low-power, long-distance integrated circuits (ICs). In addition, the preamble is insensitive to common signals and impairments (common noise, DC, spike noise, narrowband interference and spurious, channel fading, pulses, etc.).

[0063] The preamble can present ideal shaping in time / frequency (accommodating RF constraints, including low power variation in time, i.e. limited PAPR, and good spectral positioning in frequency), be customizable, as in the global spectrum / duration and number of repetition blocks to achieve the desired sensitivity, using appropriate schemes to further extend identification and interference mitigation capabilities without having to increase receiver complexity (scalable).

[0064] Certain embodiments conform to the IEEE 802.15.4 framework / specification and can be considered as an Orthogonal Frequency Division Multiplexing (OFDM) based solution. In addition, the preamble is future proof (e.g., identification / group capabilities can be extended while still appropriately spreading the energy over the allocated spectrum and duration, providing another multiple access dimension with sequence ramps and schemes).

[0065] The preamble may be considered as a series of linearly precoded OFDM symbols without a cyclic prefix.Existing transmitters may be dynamically updated in firmware and / or software to generate packets with a preamble (and remaining packet parts) as described herein.

[0066] Incremental improvements in detection verification and synchronization recovery are key to achieving good performance while keeping the packet length as short as possible for a given distance profile / target to achieve power efficiency, network system efficiency, and reasonable packet interference mitigation.

[0067] In an embodiment, the scheme is based on one or more of the following (non-exclusive) list of operators that can be applied to each sequence / block repetition (assuming that the complex vector of samples describes the signal sequence digitally): (1) signal phase operations (including inversion or complex rotation, i.e. multiplication by ±1 or ±j); (2) signal conjugation (i.e. inversion of the imaginary part); (3) signal time reversal (playing the signal vector in the other direction); and (4) signal frequency shift operations (via a numerically controlled oscillator (NCO), i.e. multiplication by exp(±j.π.dn / N), over n=[0, ..N-1] samples). Of course, other operations may be performed in other embodiments. For example, the ramp may be a parameter of the scheme operation (like a frequency shift, and in this case may be an additional sequential frequency variation shift parameter; however, even if it is efficient for robustness and the mentioned goal / purpose, it may generally be more complex for the receiver, given that additional correlations (with different ramps over time) are to be performed.

[0068] Starting with the first preamble part (STF0), a sequence S0 is used which may have an integer ramp V0 (where ramp V is defined as the number of frequency sweeps over a given block duration N, considering a linear sweep). Ideally, one full sweep (V0=1) can be performed over the entire defined bandwidth (BW), and the sequence simply repeated. This allows simple RX processing for efficient detection in asynchronous cases (no slotted / random access, and equivalent detection regardless of time shift).

[0069] Next, the second preamble part (STF1) is formed by a sequence S1 having a default slope different from S0. In one example, by using a conjugate operation, the different default slope can be a simple reverse slope. Of course, many other options are also possible (including V1=±P / Q, such as ±1 / 2, ±1 / 4, ±2, ±3...). In one or more implementations, the second preamble part can have operations performed on it, which can be selected from an operation scheme. In a specific implementation, the operation scheme can include one or more of the following: phase shift operation (including identity and reversal); frequency shift; conjugate operation; time reversal; and ramp operation.

[0070] Note that the receiver uses the difference between the blocks in S0 and S1 to perform detection and synchronization operations. The receiver uses the ramps to derive the time and frequency shift between TX and RX (implementing a system of 2 unknowns derived from 2 equations) while reducing packet interference because the different ramps induce low interference between sequences. More complex schemes also allow additional features (besides better validation in crowded environments in unlicensed bands). For example, this operation allows early packet selection / filtering and / or network / group / user identification.

[0071] The receiver can use progressive additional information from the signal, including phase shifts in addition to modulus and frequency shifts, for refined synchronization in the final step. In this way, a good balance is achieved between performance and complexity to improve behavior and interference mitigation, while keeping the default RX process simple for low-complexity receivers and the packet length as short as possible. This also minimizes "radio pollution" and resource waste (especially if combined with scalable packet and network).

[0072] Receiver processing is simplified by selecting preamble parameters, including selection of sequence, scheme, and signal shaping / filtering. These parameters can be selected to achieve good signal shaping (time and frequency properties of simple RF processing, including low power variation over time, efficient spectrum usage, pre-shaping of the saved sequence at twice the sampling frequency (Fs), and post-processing / filtering of the final waveform).

[0073] In this way, the RX algorithm can be simplified, especially if a linear frequency sweep is used with a given well-chosen and known ramp. Furthermore, the receiver can easily handle common impairments on the received signal (without high complexity increase for robustness). In particular, some processing can be done at the minimum sampling frequency (Fs) and benefit from frequency aliasing / cycling, while other processing steps can beneficially take into account information from the input signal and / or sequence definition at twice Fs (because a half-Ts sample shift is equivalent to a fractional bin frequency shift after correlation and FFT to increase frequency analysis resolution).

[0074] Reference now Figure 2A , shows a graphical representation of grouping according to an embodiment. Figure 2A As shown in , the packet 200 includes a preamble with a separate field as described herein. More particularly, as shown, the preamble of the packet 200 consists of a first part 210, which includes a sequence repeated up to a first number of repetitions (L0 times). The value and number of repetitions of the sequence may vary depending on the specific use case. In one embodiment, the sequence (and potential number of repetitions) are known to the transmitter and the receiver, and may be pre-negotiated at least for the network. In some embodiments, the default distance assigned to the device registered on the network can be used to set the block size N, and the corresponding group associated with the device can be used to determine the bandwidth / rate and repetition scheme (e.g., operation scheme) to be included in the preamble. During the reception of the first part 210, the receiver can perform packet / preamble detection and automatic gain control. In addition, at the end of the first part 210, the receiver may have reached a point of coarse time block synchronization (still biased by the carrier frequency offset).

[0075] like Figure 2A As further illustrated in FIG. 1 , the preamble 200 also consists of a second portion 220 that includes another sequence that is also repeated and can have various scheme operations performed thereon. In some cases, the sequence values ​​in the second portion 220 are equal to the sequence values ​​in the first portion 210 (i.e., S1 is equal to S0), but have a reversed slope using a complex conjugate operator.

[0076] exist Figure 2A In the example shown in , the example scheme operation includes a conjugation or reversal operation; of course, in different embodiments, others are possible, including phase shifts and / or frequency shifts. During reception of the second portion 220, the receiver can achieve synchronization (including coarse frequency synchronization). In addition, during the second portion 220, the receiver can perform authentication (and filtering when the packet is not intended for the receiver). Thus, as Figure 2A As shown in , there may be an optional third portion 225. Figure 2A As further shown in FIG. 2 , packet 200 includes a header portion and a payload portion.

[0077] exist Figure 2A In the example of , S1 can be equal to S0 because its conjugate version is used at the beginning of STF1 (i.e., its reverse ramp V1 = -V0). In this simple example, there is no frequency shift on the repetition of the second part (simplified scheme operation), but frequency shift can be added to further improve performance and mitigate interference.

[0078] A very low slope of V1 = ±1 / Q with large Q tends to define a signal close to a narrowband tone; however, in the case of an intelligently chosen scheme, it is still more robust than a pure tone once correlated, and allows phase continuity to limit edge effects on the final filtered signal (shaping balance, e.g., PAPR vs. OoB spectrum emissions), which will have more flexibility than tones with phase modulation / shifting. The scheme may include sufficient frequency shifting operations on the preamble to spread the energy appropriately over the global spectrum to comply with the rules and improve robustness. However, for typical networks, intermediate values ​​of the slope V1 may usually be a better choice, and in case of very long distance requirements, it is preferred to increase the first block size N up to the receiver capabilities rather than increasing Q.

[0079] The choice of STF1 sequence and scheme may affect edge continuity; therefore, the vector values ​​of the scheme may be intelligently selected and phase shifted to favor phase continuity at the block edges (1st order continuity), or even frequency continuity (2nd order) if desired. Good choice of sequence, scheme, and / or block edge preprocessing prior to RF resampling / filtering can provide a good waveform with low OoB emissions (aggressive spectral masking) and low power variation (almost always constant in the useful part and less than 1dB PAPR in the worst case for common IQ modulators due to the effects of the final analog edge filtering). Direct phase modulators can also be used to generate such waveforms (e.g., complex valued polarity transitions), especially when a subset with 2nd order continuity (slowly varying phase and frequency) is considered, in order to further increase efficiency with a very simple, low-cost system when the lowest power consumption is the goal.

[0080] A scheme could be chosen to have a given frequency shift at each STF1 block, where the frequency shift is an integer value of the bin spacing in the FFT analysis, thus simplifying the inverse shift at the receiver to sum these frequency outputs for simple analysis, but limiting the frequency resolution to the bin spacing. Therefore, a scheme to have a frequency shift at each STF1 / STF2 block that is not an integer value of the bin spacing (e.g. a fractional part like quarter spacing added at each new block) can help to have a higher resolution to evaluate the frequency shift for synchronization. Furthermore, knowing roughly the SNR (obtained from the previous STF0 preamble estimate), a smoothing factor for this oversampled frequency coefficient (i.e. a noisy sampled and scaled version of the channel delay behavior) is possible before evaluating the ratio of "expected region energy / peak" to "out of region energy" (which is a good indicator of detection and residual shift).

[0081] As discussed above, in some embodiments, the ramp can be used as a parameter of the STF1 / STF2 scheme to extend the principle to further improve the performance in terms of synchronization and interference mitigation capabilities. One solution is to place the ramp factor in the parameters of the scheme. This will enable different ramps (low and high) in this part of the preamble to be used to finely estimate the frequency and time shift with higher accuracy depending on the ramp.

[0082] Depending on the implementation, the transmitter may be configured to generate the preamble in the time domain or the frequency domain. In some cases, it is fairly simple to generate the preamble at an oversampled rate (e.g., 2x) using simple predefined sequences that may be stored in a lookup table (LUT) in memory. These predefined sequences may have repetitions and a scheme applied to these repetitions (e.g., a simple complex operator as discussed above).

[0083] In memory, the sequence can be defined directly in the time domain in 2x (2N complex samples) or in the frequency domain using an FFT transform (potentially on fewer samples if nulls on the edges). The sequence can also be saved in polar coordinates instead of as IQ values ​​(although the angle is just as important for coherent correlation / aggregation of the values ​​over the whole circle 2π, the modulus can be fixed or have a different / lower resolution). The sequence stored in the LUT storage enables the signal to be pre-shaped, especially in the case of oversampling (compromise between time shaping (PAPR) and frequency shaping (OoB-mask)).

[0084] In some embodiments, the transmitter may include a reshaping filter in the digital front-end circuitry that is optimized to limit PAPR or OoB emissions. Since the sequence blocks are already pre-shaped at a given sampling rate (e.g., 2x), additional block edge pre-processing may be beneficially performed at that rate before these filtering / upsampling stages.

[0085] Reference now Figure 2B-2C , shows examples of preambles of different distances using an embodiment. As illustrated, in a first example, the preamble 250 includes a first portion 260 formed by a sequence S0 repeated multiple times. The preamble 250 also includes a second portion 260 formed by a signature having a different scheme (conjugation as shown) performed thereon. Thereafter, a header and data portion 270 are transmitted.

[0086] Figure 2CA second example of a preamble 280 is illustrated, which includes a first portion 285 formed by a sequence S0 repeated multiple times. The preamble 280 also includes a second portion 290 formed by a signature with different schemes performed thereon (conjugation and reversal as shown). The I sequence in the preamble 280 can be formed by more samples than the samples in the preamble 250, because the preamble 280 will be used in a longer distance environment; the slope can be lower to achieve a longer distance (e.g., using a twice-length block N, and / or using a lower preamble BW and associated sampling frequency). Thereafter, a header and data portion 295 is transmitted.

[0087] With this arrangement, the first part of the preamble can be used for simple detection based on repetition, while the signature of the second part can be used for global verification, including synchronization, group detection / verification, and potentially further for ID selection / filtering capabilities (further verification, service / user / group ID).

[0088] In other embodiments, instead of a repetitive scanning sequence of STF0 with frequency discontinuity at the RF level, other preamble arrangements are possible. For example, in other embodiments, these RF constraints can be reduced by focusing on signals that are continuous in 2nd order (i.e., in phase and frequency) over the entire preamble, thereby limiting the possible combinations of groups (for simultaneous packet orthogonality), but still providing a good balance between low power, low cost, and global network capacity for most long-distance applications.

[0089] In such embodiments, the preamble waveform has continuity of phase and frequency over the entire preamble; therefore, a "zigzag" scan can be used for STF 0. In these embodiments, the distance can still define the block size N and the number of blocks (the higher the distance, the longer the preamble).

[0090] More specifically, the g0 group of sub-portions defines a number of BWs (typically within 300-500kHz range) and an initial ramp direction (positive or negative sweep, i.e., conjugate or non-signal) for the first block. Subsequent sub-groups (e.g., g1, g2) can be used to refine the sequence ramps for the remainder of the preamble, as well as the considerations for this grouping. Note that in some embodiments, a subset of g0 can be attributed to downlink transmissions, and the remainder to uplink transmissions.

[0091] In one example, for the same global preamble duration, the same configuration parameters as discussed above are maintained, including the distance with N and the number of blocks. For example, distance 7 can be 18 blocks of N=512 samples at Fs (total duration of 27.6ms at 333kHz BW). However, this option limits the possible scheme combinations by ensuring phase and frequency continuity over the entire preamble.

[0092] Reference now Figure 2D and 2E , shows a graphical illustration of example preambles with short (even) and long (odd) range patterns with continuous phase and frequency over the entire preamble. With minor modifications to the RX algorithm, a continuous signal in phase and frequency can be considered using an appropriate subset of schemes over the entire preamble. This provides very good shaping in time and frequency, the possibility of generating the signal with any device / RF at very low power and cost (including using direct phase modulation), while maintaining good performance in long range networks and some groups of multiple access capabilities.

[0093] Reference now Figure 3 , a block diagram of a more detailed implementation of a transmitter according to an embodiment is shown. Depending on the implementation, the transmitter can generate signals in time or in frequency using an OFDM transmitter. As illustrated, the transmitter 300 includes various hardware, firmware, and software that form a signal processing path to generate sufficient preambles. In addition, a controller 360 is coupled to the signal processing path to determine the selection of an operation scheme for preamble formation and appropriate SS, modulation scheme, replication, and the modulated SS to be performed on the preamble sequence and / or the replication. To this end, the controller 360 can be a programmable hardware circuit that is configured to execute instructions such as can be stored in one or more non-transitory storage media.

[0094] As shown, the controller 360 can receive various parameters, including information received from the network. In an embodiment, the network information can include frame structure, distance, group, and related scheme information associated with the device. In an embodiment, the group information can be a value for users in a cell area that interferes with other signals as little as possible, thereby allowing selection of sufficient SS (including BW / slope) and schemes (avoiding waveforms that are too similar in the same area).

[0095] In one or more embodiments, the distance and group information may be used to determine the preamble format, including selecting an appropriate sequence, scheme, etc.

[0096] Therefore, from the perspective of the transmitter (e.g. Figure 3 transmitter 300), a distance setting (negotiated upon initial association of devices in the network to reduce the default worst case packet length) and potentially network / group information can be used to define the bandwidth / rate of the preamble (e.g., from 300kHz to 500kHz in steps of 33kHz) and related scan sequence parameters (for STF0, the ramp factor is + / -1, and for the next part STF1 / 2, the ramp factor can be lower to + / -1 / Q1 and + / -1 / Q2) and scheme (e.g., for STF0, a simple pure repetition, and for the second part of the preamble, a more complex combination of operators applied to the repeated S1 / S2).

[0097] Note that a given preamble bandwidth (BW), typically lower than the bandwidth of the data part (and typically associated with the highest level of group concept or network identification to mitigate interference in unlicensed bands), enables the receiver to take into account adapted RX filtering and downsampling, for a simple RX preamble algorithm that benefits from sampling frequency aliasing, with a lower sampling frequency related to the BW (or N times this BW). In this way, a low power but efficient listening mode is possible for detection, and several simultaneous BWs / networks / groups are also possible.

[0098] Lowering the preamble BW also allows handling CFO (Carrier Frequency Offset) since the transmitter and receiver are not yet aligned when out of sync. This allows a robust design without having to increase the usual system receiver filter bandwidth and typically slightly increases sensitivity for the same transmit power without really changing the shaping and still complying with regulatory constraints.

[0099] Still reference Figure 3 Based at least on the distance and the group information, the controller 360 may select from the stored different possible sequences 372 0-2 The controller 360 may select an appropriate sequence for the preamble sequence from a pool 370 (which may be a table-based memory) for generating different preamble portions, as well as the selected scheme (at least for the second portion of the preamble). The pool 370 may also store bandwidth / rate information 374, which the controller 360 may use to select an appropriate bandwidth for the preamble. Depending on the implementation, the sequence pool may be stored in non-volatile memory, where the pool is predetermined and stored as part of the firmware. In other cases, the sequence may be dynamically determined and stored, for example, in a lookup table, or even generated "on the fly" or dynamically.

[0100] The controller 360 configures the preamble generator 320 to generate at least a first portion of the preamble using the above parameters, and to determine a sequence of a second portion of the preamble. Additional generators such as the scheme operator 330 (with an example specific operator 334) are configured to apply a series of sequence * schemes to the second portion (and optional additional portions) to generate a digital signal (loop); and then transmit it to the RF front end circuit 340, which transmits the preamble, followed by the header and data portion.

[0101] Note that after the "reciped-sequences" are concatenated to generate the final waveform, additional digital processing may be performed by an optional edge processor 336, e.g., to smooth the edges before the interpolation / oversampling / filtering stages of the digital front-end circuit (as may be present in the recipe operator 330 or the RF front-end circuit 340). In this way, the signal can maintain good shaping properties after its digital-to-analog conversion, i.e., provide a good spectrum while keeping the power variation as low as possible (PAPR close to 0 dB). The RF front-end circuit 340 can use any modulator, e.g., an IQ modulator with adequate digital front-end and high frequency processing, or, e.g., a phase modulator with minimal RF processing; the signal is suitable for low-power RF and transmitters.

[0102] Note that the transmitter 300 may transmit packets as a collection of frames, where there may be different frames for preamble, header 1, header 2, and data (as examples). Each frame may have its own settings (defined by fixed / top-level common parameters and / or the previous frame). In turn, a frame may consist of a given number of blocks. For a given distance / MCS, the header typically has a fixed and known number of blocks. The data portion of a packet may be formed of a variable number of blocks (each packet having a different number of bits to be transmitted, where the data length is given in the header). Although in Figure 3 The embodiments are shown at this high level, but many variations and alternatives are possible.

[0103] Also note that the sampling frequency and bandwidth can be adjusted for the preamble. For example, Fs can be equal to the bandwidth, Figure 2B-2C The illustration is 333kHz (half the sampling frequency of IEEE 802.15.4g Option 2) and 300kHz to simplify processing, improve performance and handle frequency errors. As further shown, this bandwidth may be slightly different from the preamble of the header / data.

[0104] Additionally, the ramps may differ between range, UL / DL, and other standards to minimize interference. In an embodiment, sequence S0 typically has a full ramp over the BW of each sequence to allow continuity (in phase and "cyclic frequency" sampled at Fs) at the receiver that performs a simple correlation with the expected sequence asynchronously and at Fs, while a second sequence S1 has a different ramp than S0 (e.g., in the other direction) to allow time and frequency error estimation and associated correction at the receiver. In implementations where the preamble has a third portion, its third sequence S2 may have a different ramp than S0 and S1 (e.g., not using the full preamble BW) and a specific operating scheme for each repeating sequence.

[0105] Referring now to Table 1, an example sequence of various distances according to one implementation is shown. While these specific examples are shown, it should be understood that other sequences may be used in other implementations.

[0106] Table 1

[0107]

[0108]

[0109]

[0110] In the above table, D f is the operation that distinguishes long / short range modes (usually a predetermined given frequency shift), while D g It is the operation that distinguishes the groups (usually a frequency shift or a phase shift).

[0111] Referring now to Table 2, an example second portion of the preamble is shown, where the first portion is formed by multiple repetitions of the first sequence (S0). The second portion can be formed using a second sequence that is the conjugate of the first sequence: S1=conj(S0), or has a lower slope than the first sequence, and the processing / differentiation of potential short / long distance packets uses processing every 2 blocks for short distance and processing every 3 blocks for long distance.

[0112] Table 2

[0113]

[0114] With this arrangement, a deterministic preamble is defined (depending on distance*group, no modulation). As such, it can be optimized over time by carefully chosen frequency variations, as the following example will show.

[0115] Intelligent selection schemes achieve good waveform shaping while maintaining continuity at block edges and spreading information over most of the bandwidth. In addition, different schemes for different groups improve interference mitigation between packets, their signatures to verify detection, early packet filtering, and if necessary, fractional phase and / or frequency shifts can be used to improve estimates to simplify the estimation at the receiver.

[0116] Note that intelligent selection of TX signal parameters for different users of the network can improve operation (e.g. detection tradeoff with high robustness, identification / filtering, accurate estimation and final steps of synchronization) while keeping the TX signal with very good shaping properties (a good / ideal spectrum is as rectangular as possible with low OoB emissions while having low TX power variation over time, i.e. PAPR close to 0 dB).

[0117] In some embodiments, the verification / recovery of (a portion of) the distance and group information may be extended to the preamble of the packet for further scalability, early packet interference mitigation and identification, and global long-range system efficiency. In this case, the split between the preamble and early portion of the header (PHR) used to verify and recover these top parameters may depend on the design choice of a given network.

[0118] Reference now Figure 4 , shows a block diagram of a receiver according to an embodiment. Figure 4 As shown in , the receiver 400 is configured to receive and process the preamble information (and additional header and data portions) of the packet as described above. Although shown as separate circuits, in some cases, the transmitter and receiver can be implemented as a transceiver in a single device (and can share at least some common circuits).

[0119] As shown, incoming RF signals are received via antenna 410 and provided to RF front-end circuit 415. Front-end circuit 415 may perform various RF processing, including amplification in a low noise amplifier, filtering, down-conversion, and digitization. In turn, the resulting digital information at, for example, baseband is provided to baseband processor 420.

[0120] The baseband processor 420 may perform processing on the preamble portion of the packet to enable valid packet detection to be determined. Figure 4 s or higher sampling rates. Depending on the implementation, receiver processing can be performed in the time domain or frequency domain at a sampling rate of Fs or higher. For simple preamble processing when the frequency error at the initial stage is not known, a simple solution can be to perform correlation (received signal * expected conjugate sequence) and FFT analysis in the time domain. As a first solution, after averaging several corrected blocks, the absolute value of the FFT result is analyzed to find the maximum bin. To be more robust to time and frequency offsets, more analysis can be performed, for example, several correlation * FFT analyses of blocks every N / 2 samples. Still for better peak analysis, if the input signal or reference sequence is provided at twice the sampling rate (2Fs), a shift of 1 sample allows the receiver to analyze intermediate bin values.

[0121] It should be understood that after valid packet detection and synchronization, receiver 400 can demodulate the header and data portions of the packet (for ease of illustration, additional processing circuitry for these portions is not shown here).

[0122] At a high level, the receiver 400 operates as follows. Preamble parameters including distance / group, BW, sequence and / or scheme can be used to perform packet detection and synchronization. First, the input signal is filtered (depending on a given step in multiple iteration steps 0-N), and resampled if necessary, and correlated (one or more times) (correlated with the first expected sequence S0 at step 0, etc.). In an embodiment, these correlations are converted to the frequency domain (via FFT operations) and potentially combined over several blocks (e.g., the sum or weighted sum of their absolute values ​​for step 0 with potential high frequency errors and unknown starting blocks). The receiver 400 then analyzes key indicators over several blocks (e.g., the index of the maximum power in the FFT bin and its value) to determine the likelihood level of this first step of packet detection.

[0123] Next, the receiver 400 determines whether a valid signal is potentially detected, and if so, proceeds to the next step to further process the input signal with some adjustments, such as a first correction of the coarse estimated block start (to process each block), and optional filtering that is potentially refined. Several (one or more) correlations are then performed (with the expected sequences S0 and S1, etc.). As above, these correlations are converted to the frequency domain (via FFT operations) and can be combined over several blocks to verify detection if necessary.

[0124] A comparison can also be made to detect the switch from S0 to S1 and to remove any ambiguity about where the packet starts (due to repetitions). Based on the bin index analysis (e.g., maximum power estimation) associated with the transformations on the 2 parts (S0 and S1), 2 errors can be estimated, time shift and frequency shift between TX and RX (based on the fact that S0 and S1 have different slopes or directions, so there are 2 equations to solve for 2 unknowns). These errors are then eliminated (correcting frequency and time in the next steps). The final steps can then be performed to further verify, identify and improve synchronization (time and frequency error estimate refinement) until the end of the preamble (optionally using phase information and complex values ​​instead of absolute values, giving better synchronization at the end of the preamble).

[0125] Still reference Figure 4 , the digital information from the front end circuit 415 is provided to the region selection circuit 425. To begin preamble processing, the region selection circuit 425 is configured in a first step (on STF0) to select a region that is suitable for an equivalent channel between the transmitter and the receiver; in a noisy channel where the TX and RX frequencies do not match, the frequency may be quite large (e.g., preamble BW + / - 40ppm filtering) in order to handle potential frequency errors (CFO) and because the timing is unknown (knowledge of the block edges is not yet available).

[0126] In one or more implementations, region selection (which also partly means filtering of the desired frequency bandwidth) can be split between the RF front-end circuit 415 and the region selection circuit 425. In this way, the different stages of filtering and resampling can operate in a shared wireless medium with a lot of noise and interference (e.g., Figure 4 ). As a result, interferers can be filtered out as quickly as possible. The signal blocks can then be quite localized, e.g., narrowed BW (<500kHz and even lower) and time-constrained (e.g., a reasonable N=256 at 333kHz means 0.768ms), but using diversity and interleaving, several resources spread out in time and frequency can balance noise and interference and limit the probability of having too many lost blocks. And the filtering stages and zone selection within the RF front-end circuit 415 enable reception of sufficiently useful signals including in crowded multipath environments or with parasitics and such impairments. Utilizing such operation with front-end processing and dynamic adaptation to keep only the minimum bandwidth and time of the blocks to avoid interference, while appropriately spreading useful information about selected "signatures" that are easily filtered / distinguished and "denoised", good performance can be achieved in a wide variety of environments.

[0127] The determined region selection is provided to the slope selection circuit 430, which may include multiple correlators to perform correlations on the incoming information with the expected sequence. To this end, correlation is performed at step 0 with the conj(S0) sequence (to eliminate the S0 slope). Next, the processed information is provided to the analysis circuit 440.

[0128] In order to maintain the simplicity of the frequency cycle at Fs, even if the sequence is defined at 2x, the input signal can be filtered (for example, if the useful part is 333kHz+FreqError=+ / -40kHz, then approximately 420kHz on a 666kHz bandwidth) to reduce the noise bandwidth and partially used (for example, half of the samples are used at the Fs sampling rate). For example, one sample instead of two can be used for each block to be analyzed. This processing can be done for even samples (phase 0) and also odd samples (phase 1) with the same correlation (reference expected sequence with the same phase 0) to obtain twice the frequency resolution for analysis (better peak identification (maximum bin), better accuracy x2 for correction in the next step). In this way, better performance is achieved without destroying the cycle simplification of the FFT (keeping the block size N at a minimum).

[0129] The block processing (1 or 2 correlations * FFT = snapshot) can be done several times for each block N. In this case, a circular / continuous correlation can be performed, e.g. with a shifted start index on the reference sequence to always have the same maximum bin at the same position, simplifying the next recombination without the need for NCO shifting.

[0130] As shown, analysis circuitry 440 includes an FFT engine 442, additional processing circuitry 444 that may process the resulting FFT bins, likelihood circuitry 446 that determines the likelihood of a valid preamble detection, and decision circuitry 448 that generates a decision based on the processed information.

[0131] The FFT engine 442 is configured to transform the incoming time domain samples into the frequency domain as a plurality of FFT bins. The processing circuit 444 may analyze these FFT bins corresponding to consecutive blocks of the incoming signal to detect power peaks (looking at the absolute value to detect a signal with the appropriate slope and repetition period). In some embodiments, block window filtering may be performed before the FFT to reduce edge effects of rectangular blocks in the dimension that provides sinc oscillations in another domain. In some embodiments, several processed blocks (e.g., 4 to 8 windows of size N@Fs after the FFT) may be saved and combined (e.g., aggregation, weighted summation of absolute / complex values ​​versus each distance scheme, and removal of potential shifts and defective blocks). In this way, the receiver 400 may replay the previous block slightly at each step to still reduce the preamble length and obtain the desired preamble processing (detection / verification / synchronization in time or frequency).

[0132] Next, while the receiver 400 is listening to the channel, likelihood circuit 446 calculates likelihood values ​​over time. These likelihood decisions are provided to decision circuit 448, which identifies whether sufficient criteria are present to validate a possible packet. If so, decision circuit 448 provides the most likely location (index of the peak) to the next processing step (in a loop back to region selection circuit 425 and ramp selection circuit 430).

[0133] Now, these circuits operate at the second step (looking at the STF0 and STF1 transitions and values / positions). Although the region may still be large in frequency, the rough block edges are known from the previous peak positions to align the processed blocks. In this second step, the ramp selection circuit 430 performs a correlation with the S0 and S1 sequences. In turn, the analysis circuit 440 performs analysis based primarily on the FFT of consecutive blocks of the signal to analyze the power peaks (based on absolute values). The likelihood values ​​calculated in this step enable the detection of the transition from STF0 to STF1, thereby eliminating block ambiguity to detect coarse / block timing alignment.

[0134] More specifically, the likelihood values ​​and indices are calculated on the two sequences to obtain two different sets of indices (peak positions). Based on these 2 shift values ​​and knowing the slopes of the 2 sequences (S0 vs. S1), the frequency error (CFO) and timing error (block / sampling timing offset) between TX and RX can be determined so that they can be corrected before the next step.

[0135] To quickly summarize the synchronization estimation principle, if we call D0 and D1 the maximum estimated bins on S0 and S1 respectively (with inverse shifts if needed, depending on the given scheme), and V0 and V1 the slopes of S0 and S1 respectively, from these 4 parameters {D0, D1, V0, V1}, a block timing error estimate (to realign the start of the block) and a carrier frequency error estimate (CFO) can be determined. Based on the analyzed values ​​of the preamble (including in the complex domain, if needed to improve the absolute modulus estimate at the end of the process), the estimate can be refined, time block shift ambiguities can be eliminated, and very good verification reliability is provided.

[0136] All of this processing allows the receiver 400 to further verify whether it is a possible packet based on the preamble (if not, restart listening from step 0, otherwise continue with step 2). In the (optional) third step, the area can be further refined from the previous estimate (correcting the CFO frequency error, for example, using NCO on the input signal), and the timing can also be corrected to process each block with finer adjustments. In this third step, ramp selection (correlation) and inversion scheme operations (complex operators on the blocks, such as reversal / phase shift or NCO / frequency shift) can be performed to further analyze the signal. Note that once synchronized, (optional) refined complex processing (using phase in addition to absolute value output) around the expected area (knowing the expected frequency / shift peak) can further improve performance.

[0137] Analysis of these processes allows the receiver 400 to refine the detection probability (reducing false alarms while maintaining high detection capabilities from the first step), verify the expected packet and (optionally) filter it (if different slopes and / or schemes for different distance*groups). When it is determined that the packet is not for the receiver 400, no decoding is required, saving power and time to go back to listening at step 0 as early as possible, thereby increasing efficiency. For valid packets, the refined estimates (with more accurate position and shift estimates, including time and frequency synchronization) enable more efficient reception and processing.

[0138] In some embodiments, optional identification of subgroups may be performed (including optional frequency and / or phase shift at the end of the preamble, depending on the observed scenario) (e.g., filtering packets not intended for the receiver). Additionally, optional blind detection of short preambles against long preambles may be performed (may be useful in the uplink).

[0139] When a valid packet is detected, further portions of the packet, including the header and data portions, may be processed in the receiver 400 (including within the processing path of the baseband processor 420) before providing the resulting processed information to additional processing circuitry, including a demodulator, (optionally) a descrambler, and a decoder, which additional processing circuitry is configured to perform a set of operations that are the inverse of those performed in the modulator on the transmit side.

[0140] The operation and selection of configuration of the demodulator may be performed under the control of the controller 450, which may determine the appropriate configuration of the demodulator to perform demodulation based at least in part on information parameters including distance, group, and MCS information. Depending on the implementation, the information may be received as one or more of network information, feedback information, and / or measurement information. Based on at least some of the information parameters, the controller 450 may determine an appropriate inversion operation scheme to perform on the incoming block to enable recovery of a given symbol, as well as determine whether to perform shaping operations including edge processing, windowing, and filtering, etc. The controller 450 may be a programmable hardware circuit configured to execute instructions such as may be stored in one or more non-transitory storage media.

[0141] It should be understood that although Figure 4 This is shown at a high level, but many variations and alternatives are possible. For example, the correlation process can be performed in the frequency domain (using an FFT before correlation; remember, the digital Fourier transform of a circular correlation of two sequences is equivalent to the point-by-point multiplication of their respective digital Fourier transforms. As another example of an implementation, the correlation and FFT of each block (in 430 and 442) can be combined and replaced by a continuous correlation with accumulation.

[0142] For an embodiment, the preamble energy can be globally well distributed over the preamble bandwidth (e.g., 333 to 450 kHz), and the preamble itself is robust to interferers (including continuous wave and narrowband) and fading and frequency error / drift. It can perfectly comply with the most stringent regulations and is particularly efficient in preserving wireless resources without the need for high-complexity equipment and networks. The preamble according to an embodiment can have very low PAPR (e.g., less than 1 dB) and very low OoB emissions (e.g., greater than 50 dB suppression at 500 kHz bandwidth). Scalability of the preamble definition can be achieved by varying the sequence length and the number of repetitions / schemes, with further scalability in density (based on groups of network / service / user IDs to mitigate interference / locking).

[0143] As an example, a different / lower slope on the final step and / or a different frequency shift (fractional, specific to these preambles) can improve interference mitigation and estimation processes, including improving FFT output resolution to better estimate peaks in the analyzer if required for subsequent modulation, e.g., if the peak is between 2 bins (using intermediate bins and smoothing / filtering improves estimation).

[0144] Embodiments implementing the preamble as described herein are efficient (and low power, scalable with respect to distance / duration, user density / interference, and potentially optional RX processing) for robust packetization in real multipath channels that IoT devices may use (e.g., unlicensed bands with significant interference and potentially crowded environments), and in the presence of low-cost receivers with common impairments (DC offset, spurious and tone, time and frequency synchronization offsets).

[0145] Therefore, as described herein, the preamble generator according to an embodiment can dynamically adapt the generation of the preamble based on the characteristics of at least the group and distance information. In one example, the preamble can be generated with a first level of precision / constraint selected for the signal, including: a first part with a simple linear scan; and at least a second part with a "schemed" linear scan, thereby ensuring first-order (phase) continuity. In another example, the preamble can be generated with a second level of precision / constraint selected for the signal, including: a first part with a simple linear scan; and at least a second part with a "schemed" linear scan, thereby ensuring second-order (phase and frequency) continuity. In yet another example, the preamble can be generated with a third level of precision / constraint selected for the signal, including: a first part with a linear scan, thereby ensuring second-order continuity (phase and frequency, for example, using a "zigzag"); and at least a second part with a "schemed" linear scan, thereby ensuring second-order (phase and frequency) continuity. Note that in any of these examples, potential edge processing can occur at the block edge to smooth the signal, thereby reducing changes and tending to such continuity.

[0146] While the present disclosure has been described with respect to a limited number of implementations, those skilled in the art having the benefit of this disclosure will appreciate numerous modifications and variations therefrom. The appended claims are intended to cover all such modifications and variations.

Claims

1. A device comprising: circuitry for generating a packet having at least one of a header or a data portion and a preamble, wherein the preamble comprises a first field and a second field, the first field comprising a first sequence repeated a plurality of times, a length of the first sequence and the number of the plurality of times being based at least in part on a distance between the apparatus and a receiver; and A radio frequency (RF) front end circuit is coupled to the circuit for processing and transmitting packets.

2. The apparatus of claim 1 , further comprising a controller coupled to the circuit, wherein the controller is configured to determine parameters of the preamble based at least in part on a distance parameter and a group parameter, the parameters comprising a length of the first sequence and a number of the plurality of times to identify a network having the apparatus and the receiver.

3. The device according to claim 2, wherein: The controller is configured to pre-negotiate at least the first sequence with the receiver.

4. The device according to claim 1, wherein: The circuit is used to generate a preamble code with a first sequence, wherein the first sequence has a full slope over the bandwidth of the preamble code so as to achieve continuity of phase and discrete time-frequency blocks once sampled at a given bandwidth frequency at a receiver, and the receiver includes an asynchronous receiver to perform correlation between the first field and an expected sequence corresponding to the first sequence.

5. The device according to claim 1, wherein: The circuit is configured to generate a preamble having a second field including a second sequence repeated a second plurality of times.

6. The device according to claim 5, wherein: The circuit is to perform at least one operation according to an operation scheme on the second sequence some of the second plurality of times.

7. The device according to claim 6, wherein: The circuit is to perform at least one operation according to an operation scheme on the second sequence for some of the second plurality of times, the operation scheme comprising one or more of: Phase shift operation; Frequency shift; Conjugation operation; Time reversal; or Ramp operation.

8. The device according to claim 1, wherein: The circuit is configured to generate a first sequence having a value and a bandwidth based at least in part on the distance and a sub-portion of a group parameter, the sub-portion of the group parameter being configured to identify at least one of a network or a service having the device and the receiver to enable packet detection and mitigate interference and reduce false alarms.

9. The device according to claim 1, wherein: The circuit is configured to generate a preamble including a third field having a third sequence repeated a third plurality of times, the circuit being configured to perform at least one operation according to an operation scheme on the third sequence for at least some of the third plurality of times, wherein the third sequence is configured to enable further packet validation, enable non-intended receivers to filter the packet, and enable synchronization to retrieve time and frequency accurate estimates and alignment with the transmitter.

10. The apparatus according to claim 1, further comprising at least one memory for storing a table, the table comprising a plurality of sequences from which the first sequence is to be selected.

11. The device according to claim 1, wherein: The circuit is configured to generate a preamble having a first bandwidth that is smaller than a bandwidth of the header and the data portion.

12. A method comprising: determining, in a controller of the transmitter, a first sequence and a second sequence of preambles of the packet based at least in part on a distance between the transmitter and the receiver and a group identifier known at the transmitter and the receiver in a network including the transmitter and the receiver; forming a first portion of a preamble comprising a first plurality of repetitions of a first sequence; forming a second portion of the preamble including a second plurality of repetitions of the second sequence, including performing a plurality of operations according to the operating scheme on one or more of the second plurality of repetitions of the second sequence; as well as A radio frequency (RF) signal including a packet including a preamble is transmitted from a transmitter.

13. The method according to claim 12, further comprising: When the distance is less than a first distance, forming a first portion of the preamble including a first number of first multiple repetitions, the first sequence having a first length; and When the distance exceeds the first distance, a first part of the preamble is formed, the first part including at least one of the following: a second number of first multiple repetitions, the second number being greater than the first number; and The first sequence has a second length greater than the first length.

14. The method according to claim 12, further comprising: forming a first portion of a preamble comprising a first plurality of repetitions of a first sequence, each of the first plurality of repetitions having a first slope; and A second portion of the preamble is formed including a second plurality of repetitions of the second sequence, each of the second plurality of repetitions having a second slope, the second slope being different from the first slope.

15. The method of claim 12, further comprising performing a plurality of operations according to an operation scheme on one or more of the second plurality of repetitions of the second portion, the operation scheme comprising one or more of the following: Phase shift operation; Frequency shift; Conjugation operation; Time reversal; or Ramp operation.

16. The method according to claim 12, further comprising: determining, in a controller of the transmitter, a third sequence of the preamble based at least in part on the distance and the group identifier; and Forming a third portion of the preamble including third multiple repetitions of a third sequence includes performing at least one operation according to the operating scheme on one or more of the third multiple repetitions of the third portion, wherein the third sequence is used to enable non-intended receivers to further filter packets.

17. The method according to claim 12, further comprising: Connect the first part and the second part; and Digital processing of connected portions, including edge processing to mitigate out-of-band spectral emissions (in the frequency domain) and power variations (in the time domain).

18. A system comprising: Transceiver, including: A preamble generator, configured to generate a preamble for a packet including a preamble, a header, and a data portion, wherein the preamble comprises: A first field includes a first sequence repeated a first plurality of times, wherein: The first length of the first sequence and the number of the first plurality of times are based on a range parameter associated with a range capability between the system and the receiver; and The first sequence comprises a first ramp and a first bandwidth that depend at least in part on a set of parameters of a network comprising the system and the receiver; and A second field comprising a second sequence repeated a second number of times to provide phase continuity, wherein: the second sequence includes a second ramp, the preamble generator being operable to apply an operating scheme to at least some of a second plurality of the second sequence, the operating scheme being dependent at least in part on the group parameter; A radio frequency (RF) front end circuit for forming an RF signal including a preamble, a header, and a data portion, the RF front end circuit for transmitting the RF signal; and A non-volatile memory is used to store at least a first sequence.

19. The system of claim 18, wherein: The preamble generator is used to generate: The first field includes a first sequence including a first linear scan repeated a first plurality of times; and The second field includes a second sequence including a second linear scan repeated a second number of times to provide phase and frequency continuity.

20. The system of claim 18, wherein: The preamble generator is used to generate: the first field comprising a first sequence, the first sequence comprising a first linear scan repeated a first plurality of times, the preamble generator being operable to apply a first operating scheme to at least some of the first plurality of times of the first sequence to provide phase and frequency continuity; and The second field comprises a second sequence, wherein the second sequence comprises a second linear scan repeated a second number of times to provide phase and frequency continuity, wherein at least the second field is used to achieve multi-user and interference scaling and mitigation.

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