HK1260297B - Method, receiver and computer readable storage medium for receiving data packets - Google Patents

Description

Method for receiving data packets, receiver and computer-readable storage medium

describe

Technical Field

Embodiments relate to receivers. Other embodiments relate to methods for receiving data packets. Some embodiments relate to optimizing preambles. Some embodiments relate to interference robust detection. Some embodiments relate to preamble segmentation. Some embodiments relate to non-coherent correlation. Some embodiments relate to pilot signaling.

Background Art

A system is known for transmitting small amounts of data (e.g., sensor data) from a large number of nodes (e.g., heating, electricity, or water meters) to a base station. The base station receives (and can control) the large number of nodes. The base station has access to more computing power and more complex hardware, namely, higher-performance receivers. However, the nodes often use only inexpensive crystals, which typically have a frequency deviation of 10 ppm or more.

In the document [G. Kilian, H. Petkov, R. Psiuk, H. Lieske, F. Beer, J. Robert and A. Heuberger, “Improved coverage for low-power telemetry systems using telegram splitting”, Proceedings of 2013 European Conference on Smart Objects, Systems and Technologies (SmartSysTech), 2013], it is proposed to use telegram splitting to improve the coverage of low-power telemetry systems.

In the literature [G. Kilian, M. Breiling, H.H. Petkov, H. Lieske, F. Beer, J. Robert, and A. Heuberger, “Increasing Transmission Reliability for Telemetry Systems Using Telegram Splitting,” IEEE Transactions on Communications, vol. 63, no. 3, pp. 949-961, March 2015], it is proposed to use message splitting to improve the transmission reliability of telemetry systems.

In the document [R. De Gaudenzi, F. Giannetti and M. Luise, "Signal recognition and signature code acquisition in CDMA mobile packet communications", IEEE Transactions on Vehicular Tecohnology, vol. 47, no. 1, pp. 196-208, February 1998], signal recognition and signature code acquisition in CDMA (Code Division Multiple Access) mobile packet communications are discussed.

In the literature [J. Block and E. W. Huang, "Packet Acquisition Performance of Frequency-Hop Spread-Spectrum Systems in Partial-Band Interference", IEEE Military Communications Conference, 2007. MILCOM 2007, 2007, pp. 1-7], the packet acquisition performance of frequency hopping spread spectrum systems in partial-band interference is discussed.

WO 2013/030303 A2 proposes a battery-operated stationary sensor assembly with unidirectional data transmission.

Summary of the Invention

The object of the present invention is to provide an inventive concept which improves the communication between a transmitter and a receiver.

This object is achieved by the embodiments of the present invention.

An embodiment provides a receiver, comprising a receiving unit and a synchronization unit. The receiving unit is configured to receive a data packet including a pilot sequence. The synchronization unit is configured to correlate the pilot sequence with at least two partial reference sequences, respectively, to obtain a partial correlation result for each of the at least two partial reference sequences, the at least two partial reference sequences corresponding to a reference sequence of the pilot sequence of the data packet, wherein the synchronization unit is configured to incoherently add the partial correlation results to obtain a coarse correlation result for the data packet.

The idea of the present invention is to synchronize data packets by correlating the data packet (or the pilot sequence of the data packet) with at least two partial reference sequences (each partial reference sequence is shorter than the pilot sequence contained in the data packet) to obtain a partial correlation result for each of the at least two partial reference sequences, wherein the partial correlation results are added incoherently, thereby reducing some effects of the transmission channel of the data packet to improve the synchronization performance.

Other embodiments provide a method for receiving a data packet, comprising:

- receiving a data packet including a pilot sequence;

- correlating the pilot sequence with at least two partial reference sequences respectively to obtain partial correlation results for the at least two partial reference sequences, the at least two partial reference sequences corresponding to reference sequences of the pilot sequence of the data packet; and

- incoherently adding the partial correlation results to obtain a correlation result for the data packet.

Another embodiment provides a receiver, comprising a receiving unit and a synchronization unit. The receiving unit is configured to receive data packets (e.g., at least two data packets), wherein at least a first data packet of the data packets includes a first partial pilot sequence of at least two partial pilot sequences, and at least a second data packet of the data packets includes a second partial pilot sequence of the at least two partial pilot sequences. The synchronization unit is configured to correlate the partial pilot sequences with the at least two partial reference sequences, respectively, to obtain a partial correlation result for each of the at least two partial reference sequences. Thus, the synchronization unit is configured to incoherently add the partial correlation results to obtain a coarse correlation result for the data packets.

Other embodiments provide a method for receiving a data packet, comprising:

- receiving at least two data packets, at least a first data packet of the at least two data packets including a first portion of the at least two partial pilot sequences, and a second data packet of the at least two data packets including a second portion of the at least two partial pilot sequences;

- correlating the partial pilot sequence with the at least two partial reference sequences respectively to obtain a partial correlation result for each of the at least two partial reference sequences; and

- Incoherently adding the partial correlation results to obtain a coarse correlation result for the two data packets.

Another embodiment provides a receiver comprising a receiving unit and a synchronization unit. The receiving unit is configured to receive a data packet including a pilot sequence. The synchronization unit is configured to correlate the pilot sequence with a reference sequence to obtain a correlation result. Thus, the synchronization unit is configured to apply a weighting factor to symbols of the data packet, or to symbols of the pilot sequence, or to each symbol of the pilot sequence.

Another embodiment provides a receiver comprising a receiving unit and a synchronization unit. The receiving unit is configured to receive a data packet including a pilot sequence. The synchronization unit is configured to correlate the pilot sequence with a reference sequence to obtain a correlation result. The synchronization unit is configured to detect the data packet using a correlation window, wherein the data packet is detected by detecting the highest peak among all correlation peaks exceeding a predetermined threshold within the correlation window.

Advantageous embodiments are presented in the following examples.

In some embodiments, incoherently adding the partial correlation results comprises discarding phase information after correlation, for example by adding absolute values or absolute value squares or approximate absolute values of the partial correlation results.

In some embodiments, the synchronization unit may be configured to incoherently add the partial correlation results by adding absolute values or absolute squares or approximate absolute values of the partial correlation results.

In some embodiments, the at least two partial reference sequences can be at least two different portions of a reference sequence.

In some embodiments, the data packet may include at least two partial pilot sequences as pilot sequences.

In some embodiments, the receiving unit may be configured to receive at least two data packets, wherein only a portion of the at least two data packets include a pilot sequence, eg, the receiving unit may be configured to receive a data packet without a pilot sequence.

In some embodiments, the receiving unit may be configured to receive at least two data packets, wherein each of the at least two data packets may include a pilot sequence. The synchronization unit may be configured to correlate the pilot sequence of each of the at least two data packets with the at least two partial reference sequences, respectively, to obtain a partial correlation result for each of the at least two partial reference sequences for each of the at least two data packets, wherein the at least two partial reference sequences correspond to a reference sequence of the pilot sequence of the corresponding data packet. Furthermore, the synchronization unit may be configured to incoherently add the partial correlation results for each of the at least two data packets to obtain a coarse correlation result for each of the at least two data packets, and combine the coarse correlation results of the at least two data packets to obtain a combined coarse correlation result.

The synchronization unit may be configured to combine the coarse correlation results of the at least two data packets by using a sum or an approximation of an ideal Neyman-Pearson detector of the coarse correlation results of the at least two data packets.

In some embodiments, the at least two data packets may be parts of a message, which may be divided into at least two data packets for transmission.The receiver may further comprise a data packet combining unit configured to combine the at least two data packets to obtain a message.

The synchronization unit may further be configured to coherently add the partial correlation results to obtain a fine correlation of the data packet.

Furthermore, if the combined coarse correlation result exceeds a predetermined threshold, the synchronization unit may be further configured to coherently add the partial correlation results of each of the at least two data packets to obtain a fine correlation result for each of the at least two data packets. For example, the synchronization unit may be configured to combine the fine correlation results of the at least two data packets to obtain a combined fine correlation result.

The synchronization unit may be configured to normalize the coarse correlation results of the at least two data packets and combine the normalized coarse correlation results of the at least two data packets to obtain a coarse correlation result of the message.

Furthermore, the synchronization unit may be configured to normalize the fine correlation results of the at least two data packets and combine the normalized fine correlation results of the at least two data packets to obtain a combined fine correlation result.

In some embodiments, the synchronization unit may be configured to estimate a frequency offset of the data packets.

For example, the synchronization unit can be configured to estimate the frequency offset by oversampling in the frequency domain and parallel correlation on multiple frequencies in the case of large offsets (e.g., greater than or equal to the data rate). The correlation result with the highest peak provides the coarse frequency offset.

Furthermore, the synchronization unit may be configured to estimate the frequency offset based on the phase difference between adjacent symbols in case of small offsets (eg smaller than the data rate).

Furthermore, the synchronization unit may be configured to estimate the frequency offset directly based on the partial pilot sequences in case of sufficiently large partial pilot sequences (eg depending on the signal-to-noise ratio).

Furthermore, the synchronization unit may be configured to estimate the frequency offset based on the coarse correlation result to obtain the coarse frequency offset, or to estimate the frequency offset based on the fine correlation result to obtain the fine frequency offset.

The receiver may include a header extraction unit configured to extract header information from a data packet encoded with a phase shift of a pilot sequence by applying a frequency correction to the data packet using the estimated frequency offset and estimating a phase shift of the pilot sequence.

In some embodiments, the synchronization unit may be configured to normalize symbols of the pilot sequence to obtain a normalized pilot sequence, and correlate the normalized pilot sequence with the at least two partial reference sequences respectively.

In some embodiments, the synchronization unit may be configured to calculate a variance of partial correlation results of a data packet, and detect the data packet if the variance of the partial correlation results of the data packet is less than or equal to a predetermined threshold.

In some embodiments, the synchronization unit can be configured to apply a weighting factor to the symbols of the data packet, or to apply a separate weighting factor to the symbols of each of the at least two partial pilot sequences, or to apply a separate weighting factor to each symbol of the at least two partial pilot sequences, or to apply a separate weighting factor to each of the at least two partial reference sequences, or to apply a separate weighting factor to each symbol of the data packet.

In some embodiments, the synchronization unit may be configured to detect the correlated main lobe and the side lobe and to provide the detected main lobe as the correlation result using a known distance between the main lobe and the side lobe.

In some embodiments, the synchronization unit may be configured to detect the data packet using a correlation window, wherein the data packet is detected by detecting a highest peak among all correlation peaks exceeding a predetermined threshold within the correlation window.

Embodiments provide computationally efficient frequency-insensitive packet detection by exploiting partial correlation of preambles within a subpacket and combining over multiple subpackets.

Other embodiments provide robust transmission of (additional) header information using detection and synchronization pilots by using phase shifting to transmit a partial preamble portion of a pilot of a subpacket (partial preamble) with no or minimal impact on receiver performance.

Other embodiments provide interference robust detection.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described with reference to the accompanying drawings.

FIG1 shows a schematic block diagram of a receiver according to an embodiment;

FIG2 a shows a schematic diagram of a data packet (subpacket) according to an embodiment;

FIG2 b shows a schematic diagram of a data packet (subpacket) according to another embodiment;

FIG2 c shows a schematic diagram of a data packet (subpacket) according to another embodiment;

FIG2 d shows a schematic diagram of a data packet (subpacket) according to another embodiment;

FIG2e shows a schematic diagram of a data packet (subpacket) according to another embodiment;

FIG2 f shows a schematic diagram of a data packet (subpacket) according to another embodiment;

FIG3 shows a schematic diagram of synchronization of data packets according to EP 2914039 A1;

FIG4 shows a schematic diagram of synchronization of data packets according to an embodiment;

FIG5 shows in a graph the amplitude of the autocorrelation function of the Barker-7 code plotted over time;

FIG6 shows in a graph the magnitude of the autocorrelation function of a Barker-7 code with higher side lobes caused by an interferer plotted over time;

FIG7 a shows a schematic diagram of a data packet with two partial pilot sequences and a data sequence for three different time slots, and a long interferer covering the data packet;

FIG7 b shows in a diagram the subpacket or message width normalized received power and the normalized received power plotted over time for each of three different time slots;

FIG8 a shows a schematic diagram of a data packet with two partial pilot sequences and a data sequence for three different time slots, and a short interferer covering the data packet;

FIG8 b shows in a graph the subpacket or message width normalized received power and the normalized received power plotted over time for each of three different time slots;

FIG9 a shows a schematic diagram of a data packet with two partial pilot sequences and a data sequence for three different time slots, and a short interferer covering the data packet;

FIG9 b shows in a diagram the symbol-width normalized received power and the normalized received power plotted over time for each of three different time slots;

FIG10 is a diagram showing a plurality of data packets as part of a message divided into a plurality of data packets for transmission over a communication channel, and a schematic diagram of calculating a variance over all (or at least a portion) of the data packets according to an embodiment;

FIG11 shows a schematic diagram of three data packets according to an embodiment, each data packet having two partial pilot sequences, and a schematic diagram showing weighting of the pilot sequences by applying respective weight factors to each pilot sequence of each data packet;

FIG12 graphically illustrates the magnitude of a correlation function plotted over time according to an embodiment;

FIG13 shows a schematic diagram of a detection window according to an embodiment;

FIG14 shows a flow chart of a method for detecting data packets using a detection window according to an embodiment;

15 shows in three graphs the magnitude of correlation results plotted over time for three different time slots, and the thresholds and detection windows used to detect data packets, according to an embodiment;

FIG16 is a diagram showing a plurality of data packets as part of a message divided into a plurality of data packets for transmission over a communication channel, and a schematic diagram of calculating a partial correlation on three of the data packets according to an embodiment;

FIG17 shows a flow chart of a method for receiving data packets according to an embodiment;

FIG18 shows a schematic block diagram of a receiver according to an embodiment; and

FIG19 shows a flow chart of a method for receiving data packets according to an embodiment;

In the following description, the same or equivalent elements or elements having the same or equivalent functions are denoted by the same or equivalent reference numerals.

DETAILED DESCRIPTION

In the following description, a number of details are set forth to provide a more thorough explanation of the embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail to avoid confusion regarding the embodiments of the present invention. Furthermore, unless specifically indicated otherwise, the features of the different embodiments described below may be combined with each other.

1 shows a schematic block diagram of a receiver 100 according to an embodiment; the receiver 100 comprises a receiving unit 102 and a synchronization unit 104. The receiving unit 102 is configured to receive a data packet 106 comprising a pilot sequence 108.

For example, the receiving unit 102 may be configured to receive and demodulate a signal sent from a transmitter to the receiver 100 via a communication channel and provide a data stream including data packets 106 based thereon.

The data packet 106 may include a pilot sequence 108 and one or more data sequences 110 (not shown in FIG1 , see, for example, FIG2 ) arranged before, after, or between the pilot sequence 108. The data packet 106 may be part of a message that is divided into multiple data packets (or subpackets) for transmission.

The synchronization unit 104 is configured to correlate the pilot sequence 108 with at least two partial reference sequences 112_1 to 112_n, respectively (n may be a natural number greater than or equal to 2), to obtain partial correlation results 116_1 to 116_n for each of the at least two partial reference sequences 112_1 to 112_n, wherein the synchronization unit 104 is configured to incoherently add the partial correlation results 116_1 to 116_n to obtain a coarse correlation result 118 for the data packet 106.

For example, the synchronization unit 104 may be configured to correlate the data stream provided by the receiving unit 102 with at least two partial reference sequences 112_1 to 112_n, respectively.

Each of the at least two partial reference sequences 112_1 to 112_n may be shorter than the pilot sequence 106 of the data packet.

At least two partial reference sequences 112_1 to 112_n may correspond to reference sequence 114 of pilot sequence 108 of data packet 106, i.e., at least two partial reference sequences 112_1 to 112_n may be portions of reference sequence 114 of pilot sequence 108 of data packet 106. Assuming an ideal communication channel between transmitter and receiver 100, reference sequence 114 and pilot sequence 114 are identical. Each of at least two partial reference sequences 112_1 to 112_n may be shorter than reference sequence 114. For example, reference sequence 114 may be divided into at least two (or n) parts (or sets) to obtain at least two (or n) partial reference sequences 112_1 to 112_n, i.e., a first part of reference sequence 114 is a first of at least two partial reference sequences 112_1 to 112_n, a second part of reference sequence 114 is a second of at least two partial reference sequences 112_1 to 112_n, and so on (as applicable).

The synchronization unit 104 may be configured to incoherently add the partial correlation results by adding absolute values, or absolute squares, or approximate absolute values of the partial correlation results.

A pilot (or a sequence of pilot symbols (pilot sequence)) may be sent within a data packet or subpacket. The pilot may be used for at least one of packet detection, time synchronization, and frequency synchronization.

There are different ways to position the pilots within a subpacket, as will become clear from the following discussion of Figures 2a to 2f.

2a shows a schematic diagram of a data packet (or subpacket) 106 according to an embodiment. The data packet 106 includes a pilot sequence 108 and two data sequences 110 arranged before and after the pilot sequence 108. The symbols of the data packet 106 are indicated using a complex vector diagram, i.e., each arrow can illustrate one symbol of the modulation method used to transmit the data packet.

As shown in FIG2a , in an embodiment, the pilot sequence 108 may include at least two partial pilot sequences 108_1 to 108_n. That is, the pilot sequence 108 may be divided into at least two partial pilot sequences 108_1 to 108_n. Therefore, each of the partial pilot sequences 108_1 to 108_n may have a corresponding partial reference sequence 112_1 to 112_n. For example, the first partial reference sequence 112_1 may have a corresponding first partial pilot sequence 108_1 (that is, when the first partial reference sequence 112_1 and the first partial pilot sequence 108_1 are correlated, the correlation peak may be maximized), and the second partial reference sequence 112_2 may have a corresponding second partial pilot sequence 108_2 (that is, when the second partial reference sequence 112_2 and the second partial pilot sequence 108_2 are correlated, the correlation peak may be maximized), and so on (if applicable).

2 b shows a schematic diagram of a data packet (subpacket) 106 according to an embodiment. The data packet 106 includes two partial pilot sequences 108_1 and 108_2 and a data sequence 110 arranged between the two partial pilot sequences 108_1 and 108_2. The symbols of the data packet 106 are indicated using a complex vector diagram, that is, each arrow can illustrate one symbol of the modulation method used to transmit the data packet.

2 c shows a schematic diagram of a data packet (subpacket) 106 according to an embodiment. The data packet 106 includes two partial pilot sequences 108_1 and 108_2 and a data sequence 110 arranged between the two partial pilot sequences 108_1 and 108_2. Thus, the second partial pilot sequence 108_2 is longer than the first pilot sequence 108_1 (e.g., twice as long). The symbols of the data packet 106 are indicated using a complex vector diagram, that is, each arrow can illustrate one symbol of the modulation method used to transmit the data packet.

2d shows a schematic diagram of a data packet (subpacket) 106 according to an embodiment. The data packet 106 includes two partial pilot sequences 108_1 and 108_2 and three data sequences 110 arranged before, after, and between the two partial pilot sequences 108_1 and 108_2. The symbols of the data packet 106 are indicated using a complex vector diagram, that is, each arrow can illustrate one symbol of the modulation method used to transmit the data packet.

2e shows a schematic diagram of a data packet (subpacket) 106 according to an embodiment. The data packet 106 includes two partial pilot sequences 108_1 and 108_2 and three data sequences 110 arranged before, after, and between the two partial pilot sequences 108_1 and 108_2. The symbols of the data packet 106 are indicated using a complex vector diagram, that is, each arrow can illustrate one symbol of the modulation method used to transmit the data packet.

2f shows a schematic diagram of a data packet (or subpacket) 106 according to an embodiment. The data packet 106 includes a pilot sequence 108, which is divided (or can be divided by the receiver 100) into two partial pilot sequences 108_1 and 108_2. The symbols of the data packet 106 are indicated using a complex vector diagram, that is, each arrow can show a symbol of the modulation method used to transmit the data packet.

However, the pilot 108 does not necessarily use the same modulation scheme as the data portion 110. The pilot 108 of each data packet 106 can be divided into at least two parts, here as an example, p1 (108_1) and p2 (108_2). However, the at least two parts p1 (108_1) and p2 (108_2) do not necessarily need to be separated in time. The receiver 100 can know the signals of p1 (108_1) and p2 (108_2) over time. The signal received at the receiver 100 may be affected by channel impairments such as noise. Due to the offset of the crystals used by the transmitter and the receiver 100, the receiver 100 does not initially know the exact time, frequency shift, and phase shift of the received signal.

To detect the signal, the receiver 100 may perform a cross-correlation of the entire signals p1 (108_1) and p2 (108_2) with the received signal. This will reduce the correlation peak in the presence of a frequency offset.

EP2914039A1 proposes using sub-grouped versions to reduce these effects, as will become clear from the discussion of FIG. 3 .

In detail, FIG3 shows a schematic diagram of the synchronization of a data packet 106 according to EP 2 914 039 A1. The received data packet 106 corresponds to the data packet 106 shown in FIG2 b. However, the data packet 106 is affected by a frequency offset, which is shown in FIG3 by a rotation of the vector used to describe the symbols of the data packet.

3 shows reference sequences (or correlation sequences) 112_1 and 112_2, correlation products 115_1 and 115_2 obtained by correlating the reference sequences (or correlation sequences) 112_1 and 112_2 with the data packet 106, and a correlation result 118 which is the sum of all correlation products. Therefore, the length of the correlation peak decreases due to the frequency offset.

For larger frequency offsets, even the correlation peak of the subpacket shown in FIG2a can be reduced in a significant manner.

Detection combination partial preamble correlation

3 , the embodiment provides for detection of combined partial preamble correlation (cppc).Therefore, a non-coherent combination of at least two received partial preamble parts (rp1 , rp2 , . . . ) within a small subpacket may be used.

For example, some embodiments propose non-coherent combining of code matched filter outputs for CDMA detection.In long data streams, multiple matched filter outputs for a single CDMA symbol can be combined.

In addition, the embodiments propose different ways of non-coherently combining the correlation results of a single hop of a frequency hopping spread spectrum system. The correlation results of a single hop can be combined.

It will be clear from the following discussion that, firstly, non-coherent combining on the sub-packet (or HOP) level can be used (see Figure 4), and secondly, combining of already combined sub-packet levels can be used to produce an overall result.

Figure 4 shows a schematic diagram of the synchronization of data packets 106 according to an embodiment. The received data packet 106 corresponds to the data packet 106 shown in Figure 2b. However, the data packet 106 is affected by a frequency offset, which is shown in Figure 4 by a rotation of the vector used to describe the symbols of the data packet.

4 shows at least two partial reference sequences (or correlation sequences) rp1 (112_1) and rp2 (112_2), correlation products cp1 (115_1) and cp2 (115_2) obtained by correlating the at least two partial reference sequences (or correlation sequences) 112_1 and 112_2 with the data packet 106, partial correlation results c1 (116_1) and c2 (116_2) obtained by adding the respective correlation products cp1 (115_1) and cp2 (115_2) (for example, using the equations cp1 = rp1*conj(p1) and cp2 = rp2*conj(p2)), and a coarse correlation result spm (118) of the data packet 106 obtained by incoherently adding the partial correlation results c1 (116_1) and c2 (116_2).

In other words, as shown in FIG4 , correlation is performed between the first partial pilot sequence p1 (108_1) and the second partial pilot sequence p2 (108_2) and the first partial reference sequence rp1 (112_1) and the second partial reference sequence rp2 (112_2), respectively. This produces partial correlation results c1 (116_1) and c2 (116_2).

Furthermore, a nonlinear operation such as abs(), an approximation of abs(), or any other nonlinear operation can be applied to the partial correlation results c1(116_1) and c2(116_2) of the partial preamble portion of the subpacket, or any approximation of an ideal Neyman-Pearson detector. This produces the values 11 and 12. Adding these values produces the subpacket preamble metric spm=l1+l2. In the presence of frequency offset, spm=l1+l2 is longer than the direct correlation cdirect=abs(c1+c2), even for the subpacket shown in FIG2a.

This offers the advantage that the method is robust to frequency offsets. In the event of a large crystal offset between the transmitter and receiver, fewer subbands must be searched to find the preamble.

As mentioned above, the data packet 106 may be part of a message that is divided into multiple data packets (or sub-packets) for transmission.

The receiving unit 102 may be configured to receive at least two data packets 106, wherein each of the at least two data packets 106 includes a pilot sequence 108, wherein the at least two data packets 106 are part of a message that is transmitted in the at least two data packets 106. The synchronizing unit 104 may be configured to correlate the pilot sequence 108 of each of the at least two data packets with at least two partial reference sequences rp1 (112_1) and rp2 (112_2), respectively, wherein the at least two partial reference sequences correspond to reference sequences of the pilot sequence of the corresponding data packet 106, to obtain, for each of the at least two data packets 106, partial correlation results c1 (116_1) and c2 (116_2) for each of the at least two partial reference sequences rp1 (112_1) and rp2 (112_2). Furthermore, the synchronization unit 104 may be configured to incoherently add the partial correlation results c1 (116_1) and c2 (116_2) for each of the at least two data packets 106 to obtain a coarse correlation result spm (118) for each of the at least two data packets 106. Furthermore, the synchronization unit 104 may be configured to combine the coarse correlation results spm (118) of the at least two data packets 106 to obtain a coarse correlation result for the message.

In other words, the coarse correlation results spm (118) of the subpackets (which may also be based on only one partial correlation) can be combined into a message preamble metric (or a coarse correlation result of the message) tpm. For example, the combination can be performed by a simple summation or by other approximations of an ideal Neyman-Pearson detector.

The advantage is that it requires less computing power.

For example, 30 subpackets can be used, with two partial preambles in each subpacket, e.g., subpacket version a) shown in FIG2a repeated 15 times, and subpacket version b) shown in FIG2b repeated 15 times. Using only one summation per time step requires 60 additions, i.e., 30 subpackets multiplied by 2 partial preambles. The computational effort can be reduced if two consecutive sums are used, as proposed. In each time step, the spm can be calculated over subpacket version a) and a summation over subpacket version b). The resulting spm a) and spm b) can be stored in memory. The precomputed spm a) and spm b) can then be summed over the corresponding values stored in memory. In this case, only two precomputed additions and 30 additions are required to calculate the final sum.

The synchronization unit 104 may be further configured to, if the coarse correlation result of the message exceeds a predetermined threshold, coherently add the partial correlation results c1 (116_1) and c2 (116_2) of each of the at least two data packets 106 to obtain a fine correlation result of each of the at least two data packets 106. In addition, the synchronization unit 104 may be configured to combine the fine correlation results of the at least two data packets to obtain a fine correlation result of the message.

In other words, a first search (or stage) employing incoherent addition may be combined with a second search (or stage) employing coherent addition.

The previously described technique of non-coherently adding at least two synchronization parts of a subpacket can be used. Afterwards, the sum of all subpackets can be calculated. This value can be compared with a threshold, and if the value is above the threshold, a second correlation can be performed.

The second stage can calculate the correlation of the coherent addition of all parts within a subpacket or all hops of the message. This is done as a hypothesis test for many different hypothesized frequency offsets. The value obtained by coherently adding the subcorrelation results is also compared to a threshold. If this value is within the detection range, the start of the packet is detected. The first stage (non-coherent addition) produces a coarse frequency offset, which is required for the second stage. The second stage provides a more precise frequency offset that can be used in the following decoder.

This technique requires two stages of detection. The second correlation is more frequency-sensitive than the first, requiring more computation for different frequency offsets. To reduce computational overhead, the second correlation is performed only when a packet is detected in the first stage. Consequently, the increase in computational overhead is minimal.

This technique also provides a finer estimate of the frequency offset, which helps the decoder. The decoder saves computational power because it does not have to calculate the frequency offset again.

Use pilots to signal header information

The following embodiments describe embodiments in which pilots are used to signal header information.

The data packet 106 may include header information encoded with a phase shift of the pilot sequence 108. The receiver 100 may include a header extraction unit configured to extract the header information from the data packet by applying a frequency correction to the data packet using the estimated frequency offset of the data packet 106 and estimating the phase shift of the pilot sequence.

If combined partial preamble correlation (cppc) or other schemes are used, the performance of the preamble detector can be completely insensitive or insensitive in a way that can tolerate phase rotation of the transmitted partial pilot sequences p1 (108_1) and p2 (108_2).

The transmitter can add any phase shift phi in the range [-pi, pi] to the partial pilot sequences p1 (108_1) and p2 (108_2).

Various phase shifting schemes proposed

-p1′＝p1*exp(2*pi*phi), p2′＝p2*exp(-2*pi*phi), i.e., p1 and p2 are shifted in opposite directions;

-p1′＝p1, p2′＝p2*exp(-2*pi*phi), that is, only p2 is shifted;

-p1′＝p1*exp(2*pi*phi), p2′＝p2, that is, only p1 is shifted;

Where p1′ is a phase-shifted version of p1, and p2′ is a phase-shifted version of p2.

Furthermore, combinations of the described schemes are also possible. All differential phase modulation schemes can be used. The phase shift of all or a subset of the partial pilot sequence/subpacket can be calculated by encoding the header bits to be transmitted using a forward error correction (FEC) code, thereby obtaining the transmitter code symbol c. Golay codes, BCH codes, convolutional codes, Turbo codes, LDPC codes, or other codes can be used. The code symbol can be mapped to a phase shift phi_i for index i of the partial pilot sequence/subpacket i.

If the preamble is MSK/GMSK modulated, a phase shift from p1 to p2 is generated

Next, generation of phase shifts of partial pilot sequences p1 ( 108_1 ) and p2 ( 108_2 ) of the MSK (Minimum Shift Keying) or GMSK (Gaussian Filtered Minimum Shift Keying) modulated preamble 108 is described.

If the system uses MSK or GMSK modulation for the packets, the transmitter can be easily adapted to introduce a phase shift for part of the pilot sequence p1 (108_1) or p2 (108_2). Next we will focus on p2.

If differential MSK/GMSK is used, the first bit of p2 may be inverted, and/or the first sign of the data portion following p2 may be inverted, if present.

If precoded MSK/GMSK is used, all signs of p2 may be inverted.

Decoding the received phase shift

The receiver 100 (or synchronization unit 104) may be configured to:

1. Perform a rough estimate of the frequency offset f_r of the received signal by examining part of the preamble (e.g., the phase difference of the received symbols in cp1 and cp2 can be analyzed);

2. Perform coarse frequency correction rp1′=rp1*exp(-2*p*f_r) and rp2′=rp2*exp(-2*p*f_r)

3. Estimate the phase shift phi′ between rp1′ and rp2′ (e.g., by computing phi′=arg(c1*conj(c2)), noting that p1 and p2 can be designed so that in most cases a rough frequency correction is sufficient to estimate phi′ without phase ambiguity);

4. Compute the log-likelihood llr_i, or a simplified estimate of the transmitted phi_i; and

5. Decode the transport header bit vector h_e in llr_i through the channel decoder.

Remove the transmission phase shift in the preamble

When the vector h_e has been decoded at the receiver, it can be encoded again. This gives a list of phase shifts phi_e_i.

This phase shift phi_e_i can be used to remove the phase shift of the received portion of the preamble (here rp2) in the received signal. Thus, the decoder can continue decoding the received subpackets in the same way as without transmitting the header information.

Interference robust detection

Transmissions are typically performed in unlicensed frequency bands (e.g., the ISM (Industrial, Scientific, and Medical) band) and/or the sensor nodes are not synchronized with the base station. Consequently, interference with other systems using the same time slots can occur. If the system is not synchronized with the base station, interference with other sensor nodes can also occur.

This interference negatively impacts the detection performance in the receiver. On the one hand, it reduces the correlation results of the mainlobe correlation, and on the other hand, it increases unwanted sidelobes. These sidelobes are shown in Figure 5 for a Barker code of length 7. Sidelobes are peaks that are not in the middle of the autocorrelation function and are not equal to zero.

To avoid false detections at the sidelobes, the threshold must be larger than the highest sidelobe.

The values are calculated in the autocorrelation function 13 so that one time slot is equal to one symbol time. It is also possible to use more time slots (e.g. one time slot is equal to 1/2 symbol time) or fewer time slots (e.g. one time slot is equal to 2 symbol times).

If a high-power interferer is in the air at the receiver, the correlation result at that time slot is often very high and a false detection can occur. This is shown in Figure 6. The interferer increases the correlation result and creates an "interference peak," so that the value is above the defined threshold, which leads to a false detection.

In the case of interference and/or for non-ideal correlation sequences, there are some techniques to reduce the number of false detections, which are described below. They can be used individually or in combination to achieve better results.

Normalization

If interference occurs in the frequency band used by the useful signal, the transmitted symbols may be distorted. In this case, the distortion is any phase and amplitude offset on each symbol during the transmission time of the interferer.

To reduce the impact of this interference, normalization is performed. This nonlinear operation makes the power in a subpacket, message, or each transmitted symbol equal.

In other words, for subpacket-by-subpacket normalization, for example, calculating the average power over the length of one subpacket, this calculation is performed separately for each time slot. Pmean[m] = sum(Pin)/N (Pin is the power of symbols within the subpacket length, N is the length of one subpacket in symbols, and m is the index of each time slot).

This value applies to all symbols of one subpacket length within the corresponding time slot. For example, the received power of each symbol is divided by the average power of one subpacket (Pout[k]=Pin[k]/Pmean[m], k=number of symbols in the subpacket length).

7a shows a schematic diagram of a data packet 106 having two partial pilot sequences 108_1 and 108_2 and a data sequence 110, wherein the data packet 106 is covered (or superimposed) by a long interferer 130. FIG7b shows a diagram of the received power and the normalized received power plotted over time for each of the three time slots of FIG7a.

In detail, Figures 7a and 7b illustrate this technique using three different time slots. For each time slot, the length of a subpacket, expressed in symbols, is cut. The second time slot shows a complete time slot, where all symbols of the subpacket fall within the cutout region. The first and last time slots are either too early or too late.

Over all three time slots, the interferer is active the entire time and it is assumed that the power of the interferer is much higher than the symbol power. In all three cases in the diagram of FIG7 b , the received power (the sum of the signal plus the interferer in the used frequency band) is shown as line 132.

After slicing, the average power is calculated for each time slot using the equation above. In each time slot, each symbol is divided by the average power value described by the equation above. Therefore, the average power in each time slot is now equal to 1. If there were no interferers during over-the-air transmission, the normalized average power would also be equal to 1. The impact on the fully interfered subpacket and the uninterrupted subpacket is now the same. For all three cases in the graph of FIG. 7 b , the normalized received power is shown as line 134.

It's also possible to calculate the normalization value for a length that exceeds one subpacket, for example, the length of two subpackets. In this case, we also cut the length by 1/2 before and after the subpacket. The longer the length used to calculate the normalization value, the better the results for short interferers. Short interferers only increase the subset of symbols in the area used for calculation. If only a small subset of symbols is interfered with, the impact of these symbols is minimal.

This approach works well if the duration of the interferer is much longer than the duration of one subpacket. However, if the duration is within the same region or shorter than the subpacket duration, this normalization will produce unusable results. This issue is explained using the examples in Figures 8a and 8b.

8a shows a schematic diagram of a data packet 106 having two partial pilot sequences 108_1 and 108_2 and a data sequence 110, wherein the data packet 106 is covered (or superimposed) by a short interferer 130. FIG8b shows the received power and normalized received power plotted over time for each of the three time slots of FIG8a. In all three cases in the diagram of FIG8b, the received power (the sum of the signal plus the interferer in the used frequency band) is shown as line 132. In all three cases in the diagram of FIG8b, the normalized received power is shown as line 134.

As shown in Figures 8a and 8b, the interferer 130 is only active for a portion of the subpacket duration, so not all symbols have the same received power.

A normalization factor is calculated for all symbols in that time slot. This factor is then applied to all symbols within the subpacket length. Therefore, after normalization, the interfered symbols have a much higher amplitude.

In the first time slot, the interferer only contributes to a small subset of valid symbols, and the influence of the interferer power in the normalization factor is very low. In the other two cases, the interferer's influence is greater. Normalization reduces all symbols in that time slot so that the average power distribution within that time slot is 1. Uninterrupted symbols are reduced in power just as much as the interfered symbols. Consequently, in the correlation, the correct symbol is suppressed and becomes lower than the interfered symbol. The normalized output is shown by line 134 in Figure 8b. If the interfered symbol has a greater influence on the correlation result, an incorrect detection can be made.

If the interferer length is unknown, or is not much larger than the subpacket duration, normalization can be performed on a symbol-by-symbol basis to address the issues described previously.

In addition to the normalization factor, per-symbol and per-subpacket normalizations are also useful. These are calculated for each symbol within the subpacket length, rather than just for the entire subpacket length. Figures 9a and 9b illustrate this technique.

9a shows a schematic diagram of a data packet 106 having two partial pilot sequences 108_1 and 108_2 and a data sequence 110, wherein the data packet 106 is covered (or superimposed) by a short interferer 130. FIG9b shows the received power and normalized received power plotted over time for each of the three time slots of FIG9a. In all three cases in the diagram of FIG9b, the received power (the sum of the signal plus the interferer in the used frequency band) is shown as line 132. In all three cases in the diagram of FIG9b, the normalized received power is shown as line 134.

Each symbol is normalized to the same power, for example, by dividing by its own symbol power. Furthermore, the correlated output depends only on the received phase of the synchronization sequence.

In the correlation, all signs are suppressed to be equal and are less affected by interfering signs than without normalization.

Instead of normalizing before correlation, the correlation product can be normalized.

The correlation product can be derived in each time slot using cp1=rp1*conj(p1), where rp1 is the received synchronization (or pilot) sequence, p1 is the known ideal synchronization (or pilot) sequence, and cp1 is the correlation result. As previously mentioned, this technique can be performed using a single correlation over the entire sequence, or it can be performed using sub-correlations.

However, the output signal cp1 may not provide any clear information whether a signal is present, since a strong noise pulse may also result in a high level of cp1. Therefore, one possibility is to normalize the output signal by norm1 = abs(rp1)*abs(p1).

The normalized output is then given by cplnorm = cp1 / norm1. If the pilot sequence 108 has constant power (which is assumed below), the value of cplnorm can take values from 0 to 1. A value of 1 indicates perfect correlation. In the case where the signal does not include signal p1, the absolute value of cp1 will always be less than norm1.

Alternatively, norm1 can be calculated as norm1=abs(rpl)*c, where c is a constant that can be adjusted to make cplnorm reach a maximum value of 1.

Alternatively, norm1 may be calculated as norm1=sqrt(abs(rp1^2))*c, or norm1=sqrt((abs(rp1)*abs(p1))^2).

Normalization of the input symbols can be done. Normalization is a nonlinear technique, for example, using absolute values or powers. There are different techniques depending on the interference scenario:

- Normalize on a subgroup by subgroup basis;

- Normalize on a per-message basis; and

-Normalize symbol by symbol

The advantage is that it reduces the influence of interference sources on the correlation results. Consequently, the number of false detections is reduced. If a false detection occurs, the decoder attempts to decode the packet but fails the CRC (Cyclic Redundancy Check). Reducing the number of false detections reduces CPU time usage, freeing it up for other applications and reducing device power consumption.

variance

As described above, packet detection calculates the correlation of all synchronization sequences and sums the absolute values of all sub-correlations to produce an output. If only a single sequence is used, the sequence can be divided into sub-components as described above. If the correlation value exceeds a defined threshold, a new packet is detected. This technique works well if there are no interference sources in the channel.

Another technique is based on the variance of the subgroup correlations. The variance of a discrete finite length can be calculated as var = 1/n*sum((xi - μ) ² ). The mean can be calculated as μ = 1/n*sum(xi). In this case, n is the number of subcorrelations used, μ is the previously calculated mean, and xi is the correlation result for subcorrelation i.

The partial correlation results are normalized to the received power and the length of the correlation part. Therefore, the correlation result of a sub-correlation is between 0 and 1.

If there is no noise applied and no interference sources are added to the signal, the correlation of each sub-correlation at a complete time slot produces the same value, and no variance can be observed between the correlation results of the sub-correlations. The optimal time slot is located in the middle of the autocorrelation function, where the peak has the highest value. In other time slots, there is high variance caused by unknown data.

In the figure below, as an example, the calculation of the variance for the subgroup-by-subgroup correlation is shown.

If the channel is noisy, the variance at full slots increases as the SNR decreases. Maximum variance is achieved at the lowest possible SNR, at which the packet can be correctly decoded. This value can be used as a threshold. If the calculated variance is below this threshold, the packet is detected.

This threshold can be used alone for packet detection, or can be used in combination with normal detection as a second stage to determine whether the detection in the first stage is wrong.

FIG10 is a diagram showing a plurality of data packets (or subpackets or hops) 106 as part of a message that is divided into a plurality of data packets 106 for transmission over a communication channel, and a schematic diagram of calculating variance over all (or at least a portion) of the data packets (subpackets) 106. In FIG10 , the ordinate represents frequency and the abscissa represents time.

The algorithm can also be used to detect sidelobes in the correlation that do not necessarily come from interference. For example, they can occur due to non-ideal correlation sequences.

As an example of two-stage detection, the normalized sign can be used to first calculate the correlation. If a packet is detected in the first stage, the variance of the correlation results of all sub-correlations in the detected time slot can be calculated. If the variance is less than a threshold, packet detection can be triggered.

Typically, the threshold for the first stage can be chosen to be lower than the peak of the side lobe. If a value above the threshold is detected, the variance can be calculated. Only when both values are within the detection range is a new data packet detected.

The correlation for the entire packet can be broken down into sub-correlations. If there is only one correlation sequence for the entire packet, these sub-correlations can also be used. In this case, the preamble can be split for the sub-correlations. The variance can be calculated across all sub-correlations and compared to a threshold.

The advantage of this technique is that, in the presence of interference, the number of falsely detected packets can be reduced. In addition, the threshold can be reduced, which results in a better detection rate at low SNR (Signal to Noise Ratio).

Weighted synchronization symbols

Additionally, the preamble symbols (or pilot symbols) can be weighted before correlation. There are three different techniques:

- weighting factors for all synchronization symbols;

- a weighting factor for each subpacket 106; and

- Weighting factors for each preamble part.

The weighting can also be performed after correlation has been performed on a subgroup or on a portion of the correlation sequence. Thus, a partial correlation is performed and then multiplied by a weighting factor.

As an example, the weighting factors may be calculated from the variance of the hypothesized synchronization symbols in the time slot. Alternatively, they may be obtained from the power variance of all symbols within the time slot or based on a determined signal-to-noise ratio.

Before correlation is done, weighting factors can be applied to the synchronization symbols. Interfered synchronization symbols have lower weighting factors, so these symbols have less impact on the correlation result.

11 shows a schematic diagram of three data packets 106 , each having two partial pilot sequences 108_1 and 108_2 , and shows a schematic diagram of weighting each partial pilot sequence 108_1 and 108_2 by applying respective weight factors to the pilot sequences 108_1 and 108_2 of each data packet 106 .

In other words, Figure 11 shows this concept of weighting according to the preamble part. These factors are multiplied after the preamble part summation and nonlinear operation. If the weighting is performed before correlation, the values in the figure are multiplied by the factors before the absolute value calculation is completed.

If only one correlation sequence is used, the sequence can be divided into subsequences. Therefore, each subsequence has its own weight factor.

The synchronization symbols can be multiplied by a weighting factor. It is also possible that only the preamble portion is weighted, rather than weighting each symbol. The weighting factor can be applied before correlation or after sub-correlation.

The advantage is that the number of false detections can be reduced in interfered channels, thereby reducing the power consumption of the receiver.

Sidelobe detection

Due to the non-ideal correlation sequence, sidelobes appear in the correlation output. These sidelobes are deterministic and have specific offsets relative to the main lobe. If the correlation sequence is known (which is almost always known in the receiver), the receiver can calculate these positions.

As shown in the figure below, the main lobe and two side lobes are shown. The peak values of these side lobes are lower than the main lobe. To avoid false detections, the threshold is set higher than the maximum side lobe peak value.

If the threshold is set below the highest sidelobe peak, a false detection can occur. To avoid this, the receiver looks for a higher peak within a known sidelobe time distance. If so, a sidelobe has been detected; if not, the receiver has found the mainlobe.

These side lobes can also appear at different frequency offsets. The receiver obtains the side lobes by performing an autocorrelation function at different frequency offsets.

FIG12 shows the amplitude of the correlation output plotted over time. In other words, FIG12 shows a typical correlation output. Time is plotted on the abscissa and the correlation output is shown on the ordinate. FIG12 shows a main lobe 136, two side lobes 138, and a noise floor 140.

The additional computing power is very low since the sidelobe correlation values are calculated early in the correlation and can be saved in a history (or memory).

Sidelobe detection can be done. If a value above the threshold is found, the correlation value in the sidelobe distance is compared with the actual correlation value. If the value in the sidelobe distance is higher, the sidelobe 138 is detected. Otherwise, the main lobe 136 is in the actual time slot.

This has the advantage that the detection threshold can be set below the highest peak of the side lobe 138. Thus, even for low signal-to-noise ratios, an improved detection rate can be achieved. The number of false detections can be reduced compared to the same threshold without side lobe detection.

Detection Window

As previously shown in FIG12 , there is no ideal correlation around main lobe 136. This is caused by the non-ideal correlation sequence, which separates the correlation portion into the data portion and interference. Therefore, to avoid false detection, the threshold must be set higher than the highest value outside main lobe 136, which leads to poor detection performance in noisy channels. As the SNR decreases, the value of the correlation result decreases. Packet detection is only used when the correlation value is above the defined threshold.

To achieve better noise immunity, a detection window can be introduced. This window typically has an area sized before and after the main lobe 136. If a value above a threshold is detected, the highest peak within the window is searched for, rather than directly triggering a new data packet detection. Packet detection output can be blocked until the index of the highest peak within the detection window reaches a predefined value (detection index). If the correlation value is above the threshold and the index is exactly at the defined value, packet detection can be triggered.

Figure 13 shows such a detection window. In this example, it has 11 elements. The detection index can be set in the middle of the window.

FIG14 shows a flow chart of a method 160 for detecting data packets using a detection window according to an embodiment. In a first step 162, a time slot (index) may be added. In a second step 164, a correlation may be calculated for the actual time slot. In a third step 166, the (correlation) result may be inserted into the detection window. In a fourth step 168, a maximum value in the detection window may be determined. In a fifth step 170, it may be determined whether the maximum value is greater than a threshold. If the maximum value is not greater than the threshold, the first to fifth steps 162 to 170 are repeated. If the maximum value is greater than the threshold, the index of the maximum value is determined in a sixth step 172. In a seventh step 174, it is determined whether the index is equal to the detection index. If the index is not equal to the detection index, the first to seventh steps 162 to 174 are repeated. If the index is equal to the detection index, a new packet is detected in an eighth step 176.

In other words, FIG14 shows a schematic diagram of how detection is performed. Before starting detection, a window is created and initial values are set (for example, all values are zero). Then continuous detection is started.

In a first step 162, the index of the time slot is updated. Then, a correlation is performed in the actual time slot 164. For this correlation, the above-mentioned techniques can be used, or all other techniques will work just as well. The correlation result is saved in the detection window of the latest time index 166. Therefore, the oldest one is deleted from the array (all values are shifted to the right by one and the new value is inserted on the left).

Within this window, the maximum peak is found 168. If the maximum peak within the window is below a threshold 170, processing returns to the first step 162. Otherwise, the index of the maximum value is extracted 172 and compared to the detection index 174. If the two values are the same, a new packet is detected 176.

FIG. 15 shows in three graphs the amplitude of the correlation output 170 plotted over time for three different time slots, as well as a threshold 171 and a detection window 172 for detecting data packets, in accordance with an embodiment.

In other words, Figure 15 shows this method at three different time slots. In the first part, a value above the threshold can be detected, which is not at the detection index. If a packet detection is performed in this time slot, a false detection occurs.

The highest value is obtained in the detection window 172. It is now verified whether the highest value in this window 172 is above a threshold value.

This is the case for the first time slot in Figure 15. However, the index of the highest value must be exactly the detection index, which is not the case in the first case. This index is greater than the detection index, so the peak is several steps away from the detection index. If present, it must be the highest value within the window to trigger data packet detection. Before it approaches the detection index, additional correlation values are added to the window. In this example, the index of the highest value is higher, so it is not equal to the detection index.

In the second case, the highest value is exactly at the detection index and the value is above the threshold, and group detection is used.

In the last case, the maximum value index is below the middle of the window.

If the index of the maximum value is higher than the detection index, the time slot is too early for detection and will be detected later. If the value is lower than the detection index, the packet detection has been triggered before.

A detection window 172 may be introduced. If a value above the threshold 171 is detected, packet detection is not triggered immediately. Instead, packet detection may be blocked until the index of the maximum value within the detection window 171 reaches a defined detection index.

The advantage is that the threshold can be set lower, which results in better detection rates at low SNRs, with fewer false detections.

Partially related

Instead of calculating correlations over all sub-correlations, it is possible to calculate correlations over only a portion of the total correlation sequence. This technique also works if only one correlation sequence is used. In this case, the correlation sequence can be divided into sub-parts as described above.

FIG16 is a diagram showing a plurality of data packets (or subpackets or hops) 106 as part of a message that is divided into a plurality of data packets 106 for transmission over a communication channel, and a partial correlation diagram of all three data packets (subpackets) 106. In FIG16 , the ordinate represents frequency and the abscissa represents time.

In other words, Figure 16 shows an example of this technique for correlating by subgroup. Instead of calculating correlations across all subgroups, correlations can be calculated across only three subgroups. The sum of the subsets then produces the correlation output.

The threshold value may be adapted for a lower number of sub-correlations.

Unfortunately, minimized correlation sequences have a higher probability of false detection due to interference or noise. To achieve improved (or even optimal) performance, a two-stage decision can be used. In the first step, correlation can be performed on a subset of the correlation sequence. If a packet is detected in the first step, correlation can be performed on all correlation parts in the second step. Packet detection can only be triggered if the second correlation is also above a threshold.

The correlation output of the first stage can be used to calculate the overall correlation. Therefore, the correlation is calculated on the remaining correlation sequence and added to the result of the first stage.

The correlation may be calculated on only a subset of the synchronization sequences. If a packet is detected by this method, a second correlation may be performed on all sequences.

The advantage is that the power consumption of the receiver can be reduced because the algorithm does not calculate the correlation of all components. The entire correlation is only calculated when a sub-correlation detects a packet.

method

17 shows a flow chart of a method 200 for receiving a data packet. The method comprises: step 202, receiving a data packet including a pilot sequence; step 204, correlating the pilot sequence with at least two partial reference sequences respectively to obtain partial correlation results for the at least two partial reference sequences, wherein the at least two partial reference sequences correspond to reference sequences of the pilot sequence of the data packet; and step 206, incoherently adding the partial correlation results to obtain a correlation result for the data packet.

Although some aspects have been described in the context of an apparatus, it will be clear that these aspects also represent descriptions of corresponding methods, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method step also represent descriptions of the features of the corresponding block or item or corresponding apparatus. Some or all of the method steps may be performed by (or using) a hardware device (such as a microprocessor, a programmable computer, or an electronic circuit). In some embodiments, one or more of the most important method steps may be performed by such a device.

Other embodiments

18 shows a schematic block diagram of a receiver 100 according to an embodiment; the receiver 100 includes a receiving unit 102 and a synchronization unit 104. The receiving unit 102 is configured to receive data packets 106 (e.g., at least two data packets), at least two of the data packets 106 (e.g., each of the at least two data packets) including a partial pilot sequence of at least two partial pilot sequences (note that the receiver can receive additional data packets without partial pilot sequences).

For example, the receiving unit 102 may be configured to receive and demodulate a signal sent from a transmitter to the receiver 100 via a communication channel and provide a data stream comprising at least two data packets 106 based thereon.

A first data packet 106 of the at least two data packets 106 may include a first partial pilot sequence 108_1 of the at least two partial pilot sequences 108_1-108_n, and a second data packet 106 may include a second partial pilot sequence 108_2 of the at least two partial pilot sequences 108_1-108. In addition, the at least two data packets 106 may include one or more data sequences 110 arranged before or after the partial pilot sequences 108_1 and 108_2.

The synchronization unit 104 is configured to correlate the partial pilot sequences 108_1-108_n with the at least two partial reference sequences 112_1-112_n, respectively, to obtain partial correlation results 116_1-116_n for each of the at least two partial reference sequences 112_1-112_n, wherein the synchronization unit 104 is configured to incoherently add the partial correlation results 112_1-112_n to obtain a coarse correlation result 118 for the two data packets 106.

For example, the synchronization unit 104 may be configured to correlate the partial pilot sequence 108_1 of the first data packet 106 with the first partial reference sequence 112_1 to obtain a partial correlation result 116_1 for the first partial reference sequence 112_1, and to correlate the partial pilot sequence 108_2 of the second data packet 106 with the second partial reference sequence 112_2 to obtain a partial correlation result 116_2 for the second partial reference sequence 112_2.

The synchronization unit 104 may be configured to incoherently add the partial correlation results 116_1 - 116_n by adding their absolute values or absolute value squares or approximate absolute values or any other non-linear operation.

The at least two partial reference sequences 112_1-112_n may be at least two different parts of the reference sequence 114 , and the at least two partial pilot sequences 108_1-108_n may be at least two different parts of the pilot sequence 108 .

Thus, compared to the embodiment of the receiver 100 described with reference to Figures 1 to 16, instead of a data packet 106 including at least two partial pilot sequences 108_1-108_n, data packets 106 (e.g., at least two data packets) are received, wherein at least two of the data packets 106 (e.g., each of the at least two data packets) include a partial pilot sequence from the at least two partial pilot sequences. However, the functionality of the synchronization unit 104 is essentially the same, i.e., the partial correlation results 116_1-116_n may be non-coherently added to obtain a coarse correlation result 118. If at least two other data packets are received, the partial correlation results of the at least two other data packets may be non-coherently added in the same manner to obtain a coarse correlation result for the at least two other data packets. Furthermore, the coarse correlation results of the at least two data packets and the at least two other data packets may be combined to obtain a combined coarse correlation result.

It is obvious that the description of the receiver shown and explained with reference to Figures 1 to 16 can also be applied to the receiver shown in Figure 18, and vice versa.

FIG19 shows a flow chart of a receiving method 210. The method 210 includes: step 212 of receiving data packets (e.g., at least two data packets), wherein at least two of the data packets (e.g., each of the at least two data packets) include partial pilot sequences from at least two partial pilot sequences; step 214 of correlating the partial pilot sequences with the at least two partial reference sequences to obtain partial correlation results for each of the at least two partial reference sequences; and step 216 of incoherently adding the partial correlation results to obtain a coarse correlation result for the two data packets.

Overview

The embodiments can be used in systems that transmit small amounts of data (e.g., sensor data) from a large number of nodes (e.g., heating, electricity, or water meters) to a base station. The base station receives (and can control) a large number of nodes. The base station has access to more computing power and more complex hardware, i.e., higher-performance receivers. In the nodes, only inexpensive crystals are available, typically with a frequency offset of 10 ppm or higher. However, the embodiments can also be applied to other application scenarios.

Embodiments provide multiple optimized preamble (or pilot sequence) partitions that improve interferer robustness.

The embodiment provides a correlation method that is robust to frequency offsets. Therefore, partial correlation is used and then incoherently added. The incoherent addition of the partial correlations can be used to send other information in the preamble, such as length information.

The embodiments provide several methods by which packet detection can be performed with good performance even if the communication channel is disturbed. Some of these methods achieve additional gain relative to noise.

Depending on certain implementation requirements, embodiments of the present invention may be implemented in hardware or in software. Implementation may be performed using a digital storage medium (e.g., a floppy disk, DVD, Blu-ray, CD, ROM, PROM, EPROM, EEPROM, or flash memory) having stored thereon electronically readable control signals that cooperate (or are capable of cooperating) with a programmable computer system to perform the corresponding method. Thus, the digital storage medium may be computer-readable.

Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer.The program code may, for example, be stored on a machine-readable carrier.

Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further embodiment of the inventive method is therefore a data carrier (or a digital storage medium or a computer-readable medium) having recorded thereon the computer program for performing one of the methods described herein. The data carrier, digital storage medium or recorded medium is typically tangible and/or non-transitory.

Therefore, another embodiment of the method of the present invention is a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals can, for example, be configured to be transmitted via a data communication connection (for example, via the Internet).

A further embodiment comprises a processing means, for example a computer or a programmable logic device, configured to or adapted to perform one of the methods described herein.

A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

Another embodiment according to the present invention comprises an apparatus or system configured to transmit (e.g., electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may be, for example, a computer, a mobile device, a storage device, etc. The apparatus or system may, for example, comprise a file server for transmitting the computer program to the receiver.

In some embodiments, a programmable logic device (e.g., a field programmable gate array) can be used to perform some or all of the functions of the methods described herein. In some embodiments, a field programmable gate array can collaborate with a microprocessor to perform one of the methods described herein. Typically, the method is preferably performed by any hardware device.

The devices described herein may be implemented using hardware devices, or using computers, or using a combination of hardware devices and computers.

The apparatus described herein or any component of an apparatus described herein may be implemented at least partially in hardware and/or software.

The methods described herein may be performed using a hardware device, or using a computer, or using a combination of a hardware device and a computer.

Any component of a method described herein or an apparatus described herein may be performed at least in part by hardware and/or by software.

The above-described embodiments are merely illustrative of the principles of the present invention. It should be understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Accordingly, it is intended that the present invention be limited solely by the scope of the appended patent claims and not by the specific details provided by way of description and explanation of the embodiments herein.

Claims (30)

1. A receiver (100), comprising: The receiving unit (102) is configured to receive data packets (106) including pilot sequences (108); Synchronization unit (104) is configured to correlate pilot sequence (108) with at least two partial reference sequences (112_1-112_n) respectively to obtain partial correlation results (116_1-116_n) for each of the at least two partial reference sequences (112_1-112_n); The synchronization unit (104) is configured to incoherently add the partial correlation results (116_1-116_n) to obtain the coarse correlation result (118) of the data group (106). The receiving unit (102) is configured to receive at least two data packets (106), each of which includes a pilot sequence (108). The synchronization unit (104) is configured to correlate the pilot sequence (108) of each of the at least two data packets (106) with at least two partial reference sequences (112_1-112_n) corresponding to the reference sequence (114) of the pilot sequence (108) of the corresponding data packet (106), so as to obtain a partial correlation result (116_1-116_n) for each of the at least two data packets. The synchronization unit (104) is configured to incoherently add the partial correlation results (116_1-116_n) of each of the at least two data groups (106) to obtain the coarse correlation result (118) of each of the at least two data groups. The synchronization unit (104) is configured to combine the coarse correlation results (118) of the at least two data groups (106) to obtain the combined coarse correlation results. 2. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to: noncoherently add the partial correlation results (116_1-116_n) by adding the absolute value or the square of the absolute value or the approximate absolute value or any other nonlinear operation result of the partial correlation results (116_1-116_n). 3. The receiver (100) according to claim 1, wherein the at least two partial reference sequences (112_1-112_n) are at least two different parts of the reference sequence (114) of the pilot sequence (108) of the data packet (106). 4. The receiver (100) according to claim 1, wherein the data packet (106) comprises at least two partial pilot sequences (108_1-108_n) as the pilot sequence (108). 5. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to combine the coarse correlation results (118) of the at least two data packets (106) by using the sum or approximation of the ideal Neyman-Pearson detector of the coarse correlation results (118) of the at least two data packets (106). 6. The receiver (100) according to claim 1, wherein the at least two data packets (106) are part of a message that is divided into the at least two data packets (106) for transmission, wherein the receiver (100) includes a data packet (106) combining unit configured to combine the at least two data packets (106) to obtain the message. 7. The receiver (100) according to claim 1, wherein the synchronization unit (104) is further configured to coherently add the partial correlation results (116_1-116_n) to obtain a fine correlation result of the data packets (106). 8. The receiver (100) according to claim 1, wherein if the combined coarse correlation result exceeds a predetermined threshold, the synchronization unit (104) is further configured to: coherently add the partial correlation results (116_1-116_n) of each of the at least two data packets (106) to obtain a fine correlation result of each of the at least two data packets (106); The synchronization unit (104) is configured to combine the fine correlation results of the at least two data groups (106) to obtain the combined fine correlation results. 9. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to estimate the frequency offset of the data packets (106). 10. The receiver (100) according to claim 9, wherein the data packet (106) includes header information phase-shift encoded with the pilot sequence (108); The receiver (100) includes a header extraction unit configured to extract the header information from the data packet (106) by applying frequency correction to the data packet (106) using an estimated frequency offset and estimating the phase shift of the pilot sequence (108). 11. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to: normalize the coarse correlation results of the at least two partial reference sequences, and combine the normalized coarse correlation results of the at least two partial reference sequences to obtain a combined coarse correlation result. 12. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to: normalize the symbols of the pilot sequence to obtain a normalized pilot sequence, and correlate the normalized pilot sequence with the at least two partial reference sequences (112_1-112_n) respectively. 13. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to: calculate the variance of the partial correlation results (116_1-116_n) of the data packet (106), and detect the data packet (106) if the variance of the partial correlation results of the data packet (106) is less than or equal to a predetermined threshold. 14. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured as follows: Apply a weighting factor to the sign of the data group (106), or A separate weighting factor is applied to the symbols of each of the at least two partial pilot sequences (108_1-108_n) included in the data packet (106) as the pilot sequence (108), or A separate weighting factor is applied to each symbol of at least two partial pilot sequences (108_1-108_n) included in the data group (106) as the pilot sequence (108). 15. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to: detect the associated main lobe and side lobes, and use the known distance between the main lobe and side lobes to provide the detected main lobe as a correlation result. 16. The receiver (100) according to claim 1, wherein the synchronization unit (104) is configured to detect the data packet (106) using a correlation window, wherein the data packet (106) is detected by detecting the highest peak among all correlation peaks exceeding a predetermined threshold within the correlation window. 17. A receiver (100), comprising: The receiving unit (102) is configured to receive data packets (106), wherein at least a first data packet in the data packets (106) includes a first portion of a pilot sequence in at least two partial pilot sequences (108_1-108_n), and at least a second data packet in the data packets (106) includes a second portion of a pilot sequence in at least two partial pilot sequences (108_1-108_n); Synchronization unit (104) is configured to correlate the partial pilot sequence (108) with at least two partial reference sequences (112_1-112_n) respectively to obtain partial correlation results (116_1-116_n) for each of the at least two partial reference sequences (112_1-112_n); The synchronization unit (104) is configured to incoherently add some correlation results (116_1-116_n) to obtain a coarse correlation result (118) of the data group (106). The receiving unit (102) is configured to receive other data packets (106), wherein at least a first data packet in the other data packets (106) includes a first part of a pilot sequence in at least two partial pilot sequences (108_1-108_n), and at least a second data packet in the other data packets (106) includes a second part of a pilot sequence in at least two partial pilot sequences (108_1-108_n); The synchronization unit (104) is configured to correlate the partial pilot sequences (108_1-108_n) of the other data packets with at least two partial reference sequences (112_1-112_n) respectively to obtain partial correlation results (116_1-116_n) for each of the at least two partial reference sequences (112_1-112_n), wherein the synchronization unit (104) is configured to incoherently add the partial correlation results (112_1-112_n) for the other data packets (106) to obtain a coarse correlation result (118) for the other data packets (106); The synchronization unit (104) is configured to combine the coarse correlation results (118) of the data group (106) and the other data group (106) to obtain the combined coarse correlation result. 18. The receiver (100) according to claim 17, wherein the synchronization unit (104) is configured to: noncoherently add the partial correlation results (116_1-116_n) by adding the absolute value or the square of the absolute value or the approximate absolute value or any other nonlinear operation result of the partial correlation results (116_1-116_n). 19. The receiver (100) according to claim 17, wherein the at least two partial reference sequences (112_1-112_n) are at least two different parts of a reference sequence (114), and wherein the at least two partial pilot sequences (108_1-108_n) are at least two different parts of a pilot sequence (108). 20. The receiver (100) according to claim 17, wherein the synchronization unit (104) is configured to combine the coarse correlation results (118) of the data packets (106) and the other data packets (106) using the sum or approximation of the ideal Neyman-Pearson detector of the coarse correlation results (118) of the data packets (106) and the other data packets (106). 21. The receiver (100) according to claim 17, wherein the synchronization unit (104) is further configured to coherently add the partial correlation results (116_1-116_n) of the data packets to obtain a fine correlation result of the data packets (106). 22. The receiver according to claim 17, wherein if the combined coarse correlation result exceeds a predetermined threshold, the synchronization unit (104) is further configured to: coherently add the partial correlation results (116_1-116_n) of the data packets to obtain the fine correlation result of the data packets, and coherently add the partial correlation results (116_1-116_n) of the other data packets (106) to obtain the fine correlation result of the other data packets; The synchronization unit (104) is configured to combine the fine correlation results of the data group (106) and the other data groups (106) to obtain the combined fine correlation results. 23. The receiver (100) according to claim 17, wherein the synchronization unit (104) is configured to: normalize the symbols of the partial pilot sequence to obtain a normalized partial pilot sequence, and correlate the normalized partial pilot sequence with the corresponding partial reference sequences (112_1-112_n) respectively. 24. The receiver (100) according to claim 17, wherein the synchronization unit (104) is configured to: calculate the variance of the partial correlation results (116_1-116_n), and detect the data packet (106) if the variance of the partial correlation results of the data packet (106) is less than or equal to a predetermined threshold. 25. The receiver (100) according to claim 17, wherein the synchronization unit (104) is configured to: apply a weighting factor to the symbols (106) of the data packets, or apply a separate weighting factor to the symbols of each of the at least two partial pilot sequences (108_1-108_n), or apply a separate weighting factor to each symbol of the at least two partial pilot sequences. 26. The receiver (100) according to claim 17, wherein the synchronization unit (104) is configured to: detect the associated main lobe and side lobes, and use the known distance between the main lobe and side lobes to provide the detected main lobe as a correlation result. 27. The receiver (100) according to claim 17, wherein the synchronization unit (104) is configured to detect the data packet (106) using a correlation window, wherein the data packet (106) is detected by detecting the highest peak among all correlation peaks exceeding a predetermined threshold within the correlation window. 28. A method (200) for receiving data packets, comprising: Receive (202) data packets including pilot sequences; The pilot sequence is correlated with at least two partial reference sequences (204) respectively to obtain partial correlation results for the at least two partial reference sequences, the at least two partial reference sequences corresponding to the reference sequences of the pilot sequence of the data packet; and The partially correlated results are incoherently added together (206) to obtain the correlation results of the data grouping; The receiving (202) includes: receiving at least two data packets, each of the at least two data packets including a pilot sequence; The respective correlation (204) includes: respectively correlating the pilot sequence of each of the at least two data groups with at least two partial reference sequences corresponding to the reference sequence of the pilot sequence of the corresponding data group, so as to obtain a partial correlation result for each of the at least two partial reference sequences for each of the at least two data groups; The incoherent addition (206) includes: incoherently adding the partial correlation results of each of the at least two data groups to obtain the coarse correlation results of each of the at least two data groups; The method further includes: combining the coarse correlation results of the at least two data groups to obtain a combined coarse correlation result. 29. A method for receiving data packets, comprising: Receive data packets, wherein at least a first data packet in the data packets includes a first portion of a pilot sequence in at least two partial pilot sequences, and at least a second data packet in the data packets includes a second portion of a pilot sequence in at least two partial pilot sequences; The partial pilot sequence is correlated with at least two partial reference sequences respectively to obtain partial correlation results for each of the at least two partial reference sequences; and The partially correlated results are incoherently added together to obtain the coarse correlation results of the data grouping; The receiving includes: receiving other data packets, wherein at least a first data packet in the other data packets includes a first portion of a pilot sequence in at least two partial pilot sequences, and at least a second data packet in the other data packets includes a second portion of a pilot sequence in at least two partial pilot sequences; The separate correlation includes: correlating a portion of the pilot sequence in the other data packets with at least two partial reference sequences to obtain a partial correlation result for each of the at least two partial reference sequences, wherein the synchronization unit is configured to: noncoherently add the partial correlation results of the other data packets to obtain a coarse correlation result of the other data packets; The method further includes: combining the coarse correlation results of the data group with those of other data groups to obtain a combined coarse correlation result. 30. A computer-readable storage medium storing a computer program, said computer program being configured to perform the method according to claim 28 or 29 when executed.