Patent Description:
In a digital communications network, multiple access schemes are employed to allow multiple user terminals to share a limited amount of bandwidth provided by the transmission medium. Commonly used access techniques assign fixed frequencies, time slots, or code sequences to individual transmitting user terminals, which are known as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA), respectively. If, however, the user terminal only needs to use the frequency or time slot intermittently, then this access method is quite inefficient. The document <NPL> discloses Asynchronous Coded Multiple Access and Orthogonal Frequency division Multiplexing (ACMA-OFDM). It states that such signals are symbol-synchronous, but not codeblock synchronousand that symbol synchronization is necessary for OFDM operation, but in ACMA the codeblocks are not aligned with subframe timing boundaries. Codeblocks may begin at any symbol and so they are asynchronous to the subframes. The document
<NPL> discloses that Asynchronous Scrambled Coded Multiple Access (A-SCMA) transmission from different terminals is not synchronized on a timeslot basis. Asynchronous TX increases capacity because partially overlapping bursts are recovered by multi-user iterative Successive Interference Cancellation (SIC) at the receiver. A low rate LDPC code optimized for SIC is used. A user specific unique word (UW) is prepended for robust synchronization. Pilot symbols are inserted for channel estimation. The receiver locates bursts by searching for all UWs in a bank of known UWs, using correlation.

This Summary is provided to introduce a selection of concepts in a simplified form that is further described below in the Detailed Description.

A system of one or more computers can be configured to perform particular operations or actions by virtue of having software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions. One general aspect includes a method for transmitting a random-access radio frequency (RF) signal by applying Asynchronous Coded Multiple Access (ACMA) in a communication system employing Orthogonal Frequency Division Multiplexing (OFDM), the method including: providing a reference clock defining symbol-start instants; encoding an information stream as OFDM symbols using a low rate Forward Error Correction (FEC) coding suitable for Successive Interference Cancellation (SIC) to form a payload; generating a burst, including symbols, by performing an inverse fast Fourier transform on a unique word (UW) multiplexed with the payload; and synchronizing a transmission of each of the symbols of the burst with consecutive symbol-start instants. The UW includes a plurality of Zadoff-Chu (ZC) like sequences disposed in a subset of consecutive symbol-start instants of the burst. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

Implementations may include one or more of the following features. The method where each of the symbols Includes T tones, each of the plurality of ZC-like sequences is based on a prime number less than or equal to T, and each of the plurality of ZC-like sequences is cyclically extended to T sequences. The method where the UW is multiplexed with the payload by disposing the UW before the payload. The method where the burst further includes a Channel State Estimation (CSE) word multiplexed with the payload, the CSE include a ZC-like sequence, and the UW and the CSE word are used for performing a channel state estimation. The method further including scrambling the payload. The method where the reference clock further defines frames, each of the frames includes a subset of symbol-start instants, the burst is disposed in one of the frames, and a count of the symbols in the burst is less than or equal to a count of the subset of symbol-start instants of a respective frame of the frames. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

One general aspect includes a User Equipment (UE) to communicate a random-access RF signal by applying ACMA in a communication system employing OFDM, the UE including: a reference clock defining symbol-start instants; an encoder to encode an information stream as OFDM symbols using a low rate FEC coding suitable for SIC to form a payload; an inverse fast Fourier transform to generate a burst, including symbols, by transforming a unique word (UW) multiplexed with the payload; and a synchronizer to synchronize a transmission of each of the symbols of the burst with consecutive symbol-start instants. The UW includes a plurality of ZC-like sequences disposed in a subset of consecutive symbol-start instants of the burst. The UE further including an antenna to communicate the burst to a receiver. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

One general aspect includes a method for detecting a random-access burst arrival in a communication system applying ACMA employing OFDM, the method including: providing a reference clock defining symbol-start instants; receiving bursts including symbols including multiplexed ZC-like sequences and a payload; searching for ZC-like sequences at each of the symbol-start instants in the bursts; and detecting a burst arrival when symbols disposed at a subset of consecutive symbol-start instants match a UW. The symbols are OFDM symbols disposed in consecutive symbol-start instants and encoded using a low rate FEC coding suitable for SIC. In the method at least two of the bursts are at least partially concurrent. The UW includes a plurality of cyclically shifted ZC-like sequences. Each of the bursts is modulated at a common frequency over a common frequency band with a common polarization. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

Implementations may include one or more of the following features. The method where the plurality of cyclically shifted ZC-like sequences are coherently combinable. The method where the UW is multiplexed with the payload by disposing the UW before the payload. The method where each of the bursts further includes a CSE word multiplexed with the payload, the CSE include a ZC-like sequence, and the UW and the CSE word are used for performing a channel state estimation. The method further including descrambling the payload of at least one of the bursts. The method where the reference clock further defines frames, each of the frames includes a subset of symbol-start instants, one of the bursts is disposed in one of the frames, and a count of the symbols in the one of the bursts is less than or equal to a count of the subset of symbol-start instants of a respective frame of the frames. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

One general aspect includes a base station to detect a random-access burst arrival in a communication system applying ACMA employing OFDM, the base station including: a reference clock defining symbol-start instants; a receiver to receive bursts including symbols including multiplexed ZC-like sequences and a payload; and a burst detector to search for ZC-like sequences at each of the symbol-start instants in the bursts and to detect a burst arrival when symbols disposed at a subset of consecutive symbol-start instants match a UW. The symbols are OFDM symbols disposed in consecutive symbol-start instants and encoded using a low rate FEC coding suitable for SIC. At least two of the bursts are at least partially concurrent. The UW includes a plurality of cyclically shifted ZC-like sequences. Each of the bursts is modulated at a common frequency over a common frequency band with a common polarization. The base station further including an antenna to receive the bursts from a plurality of transmitters. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

Additional features will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of what is described.

In order to describe the manner in which the above-recited and other advantages and features may be obtained, a more particular description is provided below and will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments and are not, therefore, to be limiting of its scope, implementations will be described and explained with additional specificity and detail with the accompanying drawings.

Embodiments are discussed in detail below.

The terminology used herein is for describing embodiments only and is not intended to be limiting of the present disclosure. Furthermore, the use of the terms "a," "an," etc. does not denote a limitation of quantity but rather denotes the presence of at least one of the referenced items. The use of the terms "first," "second," and the like does not imply any order, but they are included to either identify individual elements or to distinguish one element from another. It will be further understood that the terms "comprises" and/or "comprising", or "includes" and/or "including" when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. Although some features may be described with respect to individual exemplary embodiments, aspects need not be limited thereto such that features from one or more exemplary embodiments may be combinable with other features from one or more exemplary embodiments.

The present teachings improve over the art. For example, the ALOHA random access technique allows each individual terminal to transmit at will in the same frequency. When the transmissions of different terminals overlap, the transmissions "collide" and thereby become irretrievably corrupted - in which event, each of the terminals chooses a randomly selected delay for re-transmission. In a further advancement of ALOHA, the terminals line up their start of transmissions on a common time marker and keep their transmission duration the same (e.g., transmitting within time slots), in which case the chance of a collision or overlapping of the transmissions of two terminals is reduced by half. This revised access technique is known as Slotted ALOHA (S-ALOHA). To further increase the probability of transmission success, Diversity Slotted ALOHA was developed, whereby a terminal transmits multiple copies of the same information in different slots (e.g., typically, two or three copies), which reduces latency at the expense of throughput or bandwidth efficiency. In yet a further advancement, Contention Resolution Diversity Slotted ALOHA (CRDSA) was developed, whereby if receiver knows the locations of the duplicated transmissions, and if one of the duplicate transmissions is received without corruption, the information is used to cancel the other copies, which thereby increases the likelihood that transmissions from other terminals will be received without collision. If the cancellation technique is used iteratively, the capacity can be improved over S-ALOHA.

As another example, the Interleave Division Multiple Access (IDMA) is a multiple access technique where the different users share the same bandwidth, and the time slots are separated by user specific interleavers. IDMA is thus a non-orthogonal multiple access technique like random waveform Code Division Multiple Access (CDMA). While IDMA is an effective technique that trades extra receiver complexity with bandwidth and power savings, in systems where the number of users is high and the block size is large, storage of a high number of long interleavers can be inefficient and thus may be undesirable. Scrambled Coded Multiple Access (SCMA) addresses this complexity by using a single scrambling sequence with different shift factors for different users without any performance penalty. Like IDMA and random waveform CDMA, SCMA is a nonorthogonal multiple access technique. While orthogonal multiple access schemes such as TDMA or FDMA are implicitly too restrictive to achieve theoretical limits in fading channels, non-orthogonal CDMA, IDMA and SCMA have the potential of achieving such limits.

Lastly, Asynchronous Coded Multiple Access (ACMA) is an asynchronous coded multiple access technique that provides random access using low rate forward error correction (FEC) coding with successive interference cancellation (SIC). Unlike S-ALOHA, Diversity S-ALOHA, CRDSA and SCMA, ACMA assumes transmissions from different terminals are not synchronized on a timeslot basis. Removing the time slot synchronization requirement enables new applications, such as remote sensing which is essentially one-way and autonomous in nature. Moreover, instead of reducing capacity as with ALOHA, allowing fully asynchronous transmission increases the capacity in that partially overlapping bursts can be recovered by the multi-user cancellation algorithm employed by the receiver. As provided in the <NPL>, when random access is combined with SIC, the performance (e.g., spectral efficiency) is improved when bursts arrive asynchronously, as opposed to synchronously as in, for example, S-ALOHA. This effect appears to be primarily because the times during which very high channel occupancy occur are typically shorter in the asynchronous system, and as long as some portion of the time during a burst (e.g., codeblock) the signal-to-interference (C/I) ratio is at an acceptable level, progress toward decoding convergence can be achieved. Further, since a low rate code is used, a favorable C/I on even a small portion of a burst can be useful.

When ACMA is applied in an OFDM system, however, the signals can be symbol-synchronous (since OFDM is a symbol-synchronized scheme), but the codeblocks are not synchronized. In other words, the codeblocks are not aligned with frame boundaries, and thus the codeblocks are asynchronous. This contrasts with existing OFDM designs (e.g., the Long-Term Evolution (LTE) terrestrial cellular standard). In LTE systems, the codeblocks are aligned to frame time boundaries. In the present approach, where ACMA is applied in an OFDM system, the codeblocks randomly start on any OFDM symbol. OFDM is a digital multi-carrier modulation scheme that extends the concept of single subcarrier modulation by using multiple subcarriers within the same single channel. OFDM employs many closely spaced orthogonal subcarriers that are transmitted in parallel (e.g., as opposed to transmitting a high-rate stream of data with a single subcarrier). Each subcarrier is modulated with a conventional digital modulation scheme at low symbol rate, and the combination of many subcarriers enables data rates similar to conventional single-carrier modulation schemes within equivalent bandwidths. OFDM is based on the FDM technique (where different streams of information are mapped onto separate parallel frequency channels, and each FDM channel is separated from the others by a frequency guard band to reduce interference between adjacent channels). With the OFDM scheme multiple subcarriers carry the information stream, where the subcarriers are orthogonal to each other, and a guard interval is added to each symbol to minimize the effect of the channel delay spread and inter-symbol interference. Accordingly, each OFDM symbol reflects multiple frequency instances.

In addition to the enhancement of spectral density provided by such asynchronous codeblock operation, the further benefit of a significantly expanded pool of available preamble codes for the detection of individual random-access bursts is achieved. In order to perform SIC, it is first necessary to detect the individual random-access burst arrivals and be able to distinguish them. Typically, some type of preamble code (e.g., unique word or UW) is added to the burst for this purpose. Further, in order to support a large user community and to prevent collisions between bursts from different users, it is necessary to have a large enough pool of preamble codes to select from. Herein, collision refers to two transmitters using the same UW at the same symbol-start instant. When the UW is disposed at the beginning of the burst, the collision occurs at burst start. In synchronous designs, this pool is limited and sets the upper limit on the number of simultaneous users supported, independent of any limits set by the FEC/SIC design (where FEC design may include low-rate coding and/or spreading, here noting that spreading is equivalent to repetition coding). Since the bursts are free to arrive at any symbol boundary (being symbol synchronous), rather than being constrained to start on a frame boundary (being codeblock asynchronous), the pool of preamble codes that can be distinguished is significantly expanded. This allows reliable operation at much higher values of simultaneous users, achieving significant improvement of the FEC/SIC design.

Further, in a true random-access system, burst arrivals are random (following, for example, a Poisson arrival process). In this case operation with a higher average loading (number of simultaneous users) provides even further gains, because by operating a higher loading the probability distribution of user arrivals is more compact. In other words, error performance is primarily limited by the occasions of peak users, and high peaks are less likely in a system designed to support high average loading as compared to lower loading.

<FIG> illustrates an exemplary frame and symbol clock according to various embodiments.

A reference clock <NUM> may be segmented into frames <NUM> along a time axis. The duration of a frame may be fixed, for example, <NUM> milliseconds. Each frame may have a frame-start instant <NUM>. The frame-start instant <NUM> may also demark a frame-end instant for an immediately preceding frame. Each frame <NUM> may be segmented into symbols <NUM> having a symbol-start instant <NUM>. The duration of a symbol may be fixed, for example, <NUM> milliseconds divided by N, where N is the count of symbol-start instants in the frame <NUM>. The symbol-start instant <NUM> may also demark a symbol-end instant for an immediately preceding symbol. Some of the symbol-start instants may be coincident with a frame-start instant.

A burst <NUM> may begin at a burst-start instant <NUM>. The burst-start instant <NUM> may not be coincident with a frame-start instant. In this example, the burst-start instant <NUM> is coincident with the second symbol-start instant <NUM> in the frame <NUM>. The burst <NUM> may include a UW <NUM> disposed in consecutive symbols. In this example, the burst <NUM> starts with the UW <NUM> or in other words is disposed before a payload <NUM>, <NUM>. The payload <NUM>, <NUM> is distributed through the burst <NUM> with an intervening CSE <NUM>. Multiple CSEs may be disposed in the burst <NUM>. The count of CSEs in the burst <NUM> may depend on a count of symbols in the burst <NUM>. The count of symbols in the burst <NUM> may determine how many CSEs are interleaved through the payload in the burst. The burst <NUM> may include a last symbol <NUM>. Each of the symbols in the burst <NUM> is synchronized with an immediately preceding symbol-start instant.

In order to perform successful burst detection and demodulation, it is necessary to perform the two different tasks, (<NUM>) detection of burst arrival, and (<NUM>) channel estimation (e.g., determine the amplitude and phase of the signal/channel, such as in a multipath fading type of environment). In accordance with example embodiments, the two tasks of burst detection and channel estimation are performed using common waveforms, which, for example, minimizes overhead. By way of example, burst detection and channel estimation are performed using a common set of OFDM symbols or sequences. By way of further example, in order to enable detection of signal arrival or burst detection (e.g., UW preamble detection) and to facilitate channel state estimation (CSE), the provided approach employs OFDM symbols that are based on Zadoff-Chu (ZC) sequences (which are hereinafter referred to as "ZC-like sequences"). Such sequences exhibit constant amplitude in both the time and frequency domains. A constant amplitude in the time domain facilitates a low Peak-to-Average Power Ratio (PAPR) for burst detection, and a constant amplitude in the frequency domain facilitates CSE.

In accordance with further example embodiments, for enhanced detection performance, the OFDM symbols are designed to be coherently combinable. By way of example, depending on the time variation of the channel (e.g., the speed of the time variation), the symbols may be located consecutively, whereby placing them consecutively allows them to be coherently combined for improved detection performance (e.g., even with moderately time-varying channels). Whereas, with slowly time-varying channels, the symbols can instead be spaced uniformly or in some other way in time along the burst.

In accordance with certain example embodiments, therefore, allowing for moderate time variation, for example, the preamble symbols are placed as the first M symbols (which are also used for CSE). Additionally, one or more further symbols can be placed at one or more respective subsequent locations (e.g., nonconsecutive with the first M symbols), which are used for only CSE. The further symbol is inserted for CSE purposes due to the time-varying nature of the channel As a further embodiment, the subsequent symbols may also be used to enhance burst detection, but perhaps by non-coherent combination with the other symbols (e.g., assuming the coherence time of the channel is shorter than the time spacing between symbols).

According to one example embodiment, each burst comprises <NUM> subcarriers (in frequency) and <NUM> OFDM symbols (in time). The first four symbols comprise ZC-like sequences for burst detection and CSE. Further, the ninth symbol may be another of the ZC-like sequences as in the first four symbols for CSE. Accordingly, in this example embodiment, the symbols [<NUM>,<NUM>,<NUM>,<NUM>] are used as a UW preamble for burst detection, and symbols [<NUM>,<NUM>,<NUM>,<NUM>,<NUM>] are used as reference symbols for CSE. Accordingly, the reuse of the UW symbols for CSE achieves significantly improved efficiency in design and performance.

According to such example embodiments, because ZC sequences with good properties are not available for non-prime lengths, the ZC sequences used for the preamble UW symbols and subsequent CSE symbols may be of a prime length and employed cyclically to extend to the desired non-prime length for the OFDM symbols (hence the terminology "ZC-like sequences" used herein). Since a prime-length ZC sequence is employed cyclically, the ideal properties of a true ZC sequence are diminished. The prime-length of the ZC sequence that is employed cyclically may be determined through appropriate design considerations and simulation to optimize the properties/performance. According to one such embodiment, ZC sequences of prime length <NUM> are cyclically extended to length <NUM> for the example embodiment of a <NUM> subcarrier OFDM symbol. Alternative embodiments, however, may be employed using cyclical extension of other prime sequence lengths. Further, in the example using a sequence length of <NUM>, there are <NUM> available sequences (there are n - <NUM> available sequences, where n is the sequence length). Further, each burst uses <NUM> sequences (for the symbols [<NUM>, <NUM>, <NUM>, <NUM>, <NUM>], and they are not to be reused - so, for this example embodiment, <NUM> of the <NUM> sequences are used to make up <NUM> different sets of <NUM> sequences (each sequence set comprises <NUM> different sequences for the symbols [<NUM>, <NUM>, <NUM>, <NUM>, <NUM>] - for example, set <NUM> employs sequences <NUM>-<NUM>, set <NUM> employs sequences <NUM>-<NUM>, set <NUM> employs sequences <NUM>-<NUM>, etc.). Further, every cyclic/shifted permutation of each sequence set may also be used (e.g., since there is time and frequency synchronization on a symbol basis, a cyclic permutation of a sequence or sequence set would also be recognized). In this example, since there are <NUM> cyclic permutations, a total of <NUM> different sequence permutations are available (<NUM> permutations x <NUM> sets). Additionally, not only are <NUM> sequences available, but they can occur in any symbol-start position (any of the synchronized symbol-start positions). Accordingly, in this example, based on the <NUM> symbols per burst, any of the <NUM> sequences can occur in any of the <NUM> symbol-start positions, resulting in a total of <NUM>,<NUM> possibilities.

According to further example embodiments, while the foregoing example reflects a design for an OFDM carrier using <NUM> subcarriers, the principles can be extended to other OFDM system designs as well.

Burst transmission and reception is asynchronous as neither is dependent on a static allocation or a feedback based dynamic allocation. As such, an allocation grant-free protocol (random access) protocol may be utilized for transmission and reception.

According to further example embodiments, for burst detection, the search for the preamble sequences over the various cyclic shifts can be searched in parallel with low complexity. By way of example, a Fast Fourier Transformation may be employed to perform cyclic correlation of each of the sequences, providing the correlation outputs for all cyclic shifts in parallel.

<FIG> illustrates a communication system applying Asynchronous Coded Multiple Access (ACMA) employing OFDM, according to various embodiments.

<FIG> illustrates a communication system <NUM> applying Asynchronous Coded Multiple Access (ACMA) employing OFDM. The communication system <NUM> may include a User Element (UE) <NUM>, a base station <NUM> and a support service <NUM>. There may be multiple UEs <NUM>, base stations <NUM> or support service <NUM>. The UE <NUM> may communicate with the base station <NUM> via an RF signal <NUM>.

The support service <NUM> may be included with the UE <NUM>, with the base station <NUM> or in a separate apparatus. In some embodiments, connections between the UE <NUM> and the support service <NUM> may not be a physical connection, as illustrated by the dashed connectors. In some embodiments, connections between the base station <NUM> and the support service <NUM> may not be a physical connection, as illustrated by the dashed connectors. The support service <NUM> may include a ZC supplier <NUM> to provide a ZC-like sequence to a CSE supplier <NUM> or a UW supplier <NUM>. The CSE supplier <NUM> and UW supplier <NUM> may arbitrate/manage ZC-like sequences provided to the UE <NUM> to be included in a burst, for example, by cyclically extending a ZC sequence, by providing a random ZC-like sequence per UE, and the like. A reference clock <NUM> may be provided to the base station <NUM> and the UE <NUM>. Timing adjustments may be provided at the UE <NUM> to account to synchronize a symbol-start between the UE <NUM> and the base station <NUM>. Timing adjustments may be provided at the base station <NUM> to account to synchronize a symbol-start between the UE <NUM> and the base station <NUM>. In some embodiments, the reference clock <NUM> may be distributed by the base station <NUM>.

The UE <NUM> may provide an information stream <NUM> that is encoded by encoder <NUM>. An output of the encoder <NUM> may be optionally provided to a scrambler <NUM> for scrambling. An output of the scrambler <NUM> is mapped by a constellation mapper to form a payload <NUM>. The payload <NUM>, a UW from the UW supplier <NUM>, and a CSE from the <NUM> are input to an inverse digital Fourier transform block that multiplexes/combines the inputs. The inverse digital Fourier transform block may include a serial to parallel block <NUM>, an Inverse Fast Fourier Transform (IFFT) block <NUM> and a parallel to serial block <NUM> to form a burst <NUM>. The burst <NUM> may be provided to a UE antenna <NUM> for transmission to the base station <NUM>.

The base station <NUM> may receive the burst <NUM> at a base antenna <NUM>. An output of the base antenna <NUM> may be presented to a digital Fourier transform block, a burst detector <NUM> and a CSE detector <NUM>. The digital Fourier transform block may include a serial to parallel block <NUM>, a Fast Fourier Transform (FFT) block <NUM> and a parallel to serial block <NUM>. An output of the digital Fourier transform block may provide samples. The samples are provided, as necessary, to a demapper <NUM>, a buffer <NUM>, a descrambler <NUM>, a decoder <NUM>, and a remodulator <NUM> to output a received information stream.

The reference clock <NUM> (post any timing adjustments) is provided to the IFFT block <NUM> and the FFT block <NUM> so that symbols of the burst <NUM> are synchronized with symbol-start instants.

<FIG> illustrates a method for transmitting a random-access Radio Frequency (RF) signal by applying ACMA in a communication system employing OFDM for transmitting, according to various embodiments.

A method <NUM> for transmitting an RF signal is described. The method <NUM> may include operation <NUM> to provide a reference clock defining symbol-start instants. The method <NUM> may include operation <NUM> to encode an information stream as OFDM symbols to form a payload. The method <NUM> may include operation <NUM> to scramble the payload. The method <NUM> may include operation <NUM> to generate a burst of symbols by performing an inverse fast Fourier transformation on multiplexed/combined set of symbols including a UW, an optional CSE word, and the payload. the encoded information stream. The method <NUM> may include operation <NUM> to synchronize a transmission of each of the symbols of the burst with consecutive symbol-start instants.

<FIG> illustrates a method for detecting a random-access Radio Frequency (RF) signal by applying ACMA in a communication system employing OFDM for receiving, according to various embodiments.

A method <NUM> for detecting a burst is described. The method <NUM> may include operation <NUM> to provide a reference signal defining symbol-start instants. The method <NUM> may include operation <NUM> to receive bursts including ZC-like sequences and a payload. The method <NUM> may include <NUM> to search for ZC-like sequences in consecutive symbol-start instants. The method <NUM> may include operation <NUM> to detect a burst arrival when consecutive symbols match a UW, wherein at least two of the bursts are at least partially concurrent. The method <NUM> may include operation <NUM> to descramble the payload.

While example embodiments of the present invention may provide for various implementations (e.g., including hardware, firmware and/or software components), and, unless stated otherwise, all functions are performed by a CPU or a processor executing computer executable program code stored in a non-transitory memory or computer-readable storage medium, the various components can be implemented in different configurations of hardware, firmware, software, and/or a combination thereof. Except as otherwise disclosed herein, the various components shown in outline or in block form in the figures are individually well known and their internal construction and operation are not critical either to the making or using of this invention or to a description of the best mode thereof.

Claim 1:
A method (<NUM>) for transmitting a random-access Radio Frequency, RF, signal by applying Asynchronous Coded Multiple Access, ACMA, in a communication system employing Orthogonal Frequency Division Multiplexing, OFDM, the method (<NUM>) comprising:
providing (<NUM>) a reference clock (<NUM>) defining symbol-start instants (<NUM>);
encoding (<NUM>) an information stream as OFDM symbols using a low rate forward error correction (FEC) coding suitable for successive interference cancellation, SIC, to form a payload (<NUM>, <NUM>);
generating (<NUM>) a burst (<NUM>), comprising symbols, by performing an Inverse Fast Fourier Transform on a Unique Word, UW, (<NUM>) multiplexed with the payload (<NUM>, <NUM>); and
synchronizing (<NUM>) a transmission of each of the symbols of the burst (<NUM>) with consecutive symbol-start instants (<NUM>),
wherein
the UW (<NUM>) comprises a plurality of Zadoff-Chu, ZC, like sequences disposed in a subset of consecutive symbol-start instants (<NUM>) of the burst (<NUM>).