Signal receiving method applied to DSSS-OQPSK and differential rake receiver

Abstract

The invention relates to the technical field of wireless communication, and discloses a signal receiving method applied to DSSS-OQPSK and a differential rake receiver, and the method comprises the following steps: carrying out multipath separation on a received signal, and sequentially carrying out the following steps on each path: a, carrying out de-spreading processing based on a direct sequence spreading code, and generating a complex symbol sequence containing a phase error; b, performing conjugate differential operation on adjacent complex symbols to eliminate phase errors, and obtaining differential symbols after the phase errors are eliminated; combining the differential symbols after the phase errors are eliminated according to the receiving power of the paths where the differential symbols are located, wherein the receiving power is obtained through channel estimation (CE); and outputting the combined demodulation signal. According to the method, energy-based combination is carried out on differential symbols output by each path, and the method is not sensitive to frequency deviation, phase deviation and sampling deviation.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and in particular, to a signal receiving method and a differential rake receiver applied to DSSS-OQPSK. Background Art

[0002] DSSS-OQPSK is a communication modulation technology that combines direct sequence spread spectrum (DSSS) and offset quadrature phase shift keying (OQPSK), and is commonly used in high-performance anti-interference and low-power wireless communication scenarios.

[0003] DSSS improves the anti-interference ability, and the constant modulus characteristic of OQPSK reduces the requirement for the linearity of the PA at the transmitting end. Therefore, it is widely used in Internet of Things protocols. The optimal demodulation algorithm for DSSS is coherent demodulation, but coherent demodulation is extremely sensitive to carrier frequency offset, phase offset, and sampling clock offset.

[0004] In order to achieve optimal performance, both the transmitting and receiving ends require high-precision crystal oscillators, and the receiving end requires high-complexity estimation algorithms, which limit the application of coherent demodulators in Internet of Things devices. Although non-coherent demodulation algorithms are not sensitive to the above-mentioned RF losses and have low implementation costs, their demodulation performance is greatly reduced. Summary of the Invention

[0005] The main purpose of the present invention is to solve the technical problem that coherent demodulation in the prior art is extremely sensitive to carrier frequency offset, phase offset, and sampling clock offset. A signal receiving method applied to DSSS-OQPSK includes the following steps:

[0006] Perform multipath separation on the received signal, and sequentially execute the following for each path:

[0007] a. Perform despreading processing based on the direct sequence spread spectrum code to generate a complex symbol sequence including phase error;

[0008] b. Perform conjugate difference operation on adjacent complex symbols to eliminate phase error, and obtain differential symbols after eliminating phase error;

[0009] Merge the differential symbols after eliminating phase error according to the received power of the path where they are located, and the received power is obtained through channel estimation (CE);

[0010] Output the demodulated signal after merging.

[0011] The second aspect of the present invention provides a differential rake receiver applied to DSSS-OQPSK, including:

[0012] A multipath separation and despreading unit, configured to perform multipath separation on the received signal, and sequentially execute the following for each path:

[0013] a. Perform despreading processing based on the direct sequence spread spectrum code to generate a complex symbol sequence containing phase errors;

[0014] b. Perform conjugate difference operation on adjacent complex symbols to eliminate phase errors and obtain differential symbols after eliminating phase errors;

[0015] A weighted combining unit is used to combine the differential symbols after eliminating phase errors according to the received power of the path where they are located, and the received power is obtained through channel estimation (CE);

[0016] An output unit is used to output the combined demodulated signal.

[0017] A third aspect of the present invention provides an electronic device, including: a memory and at least one processor. Instructions are stored in the memory, and the memory and the at least one processor are interconnected by a line; the at least one processor calls the instructions in the memory so that the electronic device executes the above-mentioned signal receiving method applied to DSSS-OQPSK.

[0018] The present invention has the following beneficial effects:

[0019] The present invention is insensitive to frequency offset, phase offset, and sampling deviation by performing energy-based combination on the differential symbols output from each path. Description of the Drawings

[0020] Figure 1 It is a schematic flowchart of the method of the present invention. Detailed Embodiments

[0021] The terms "first", "second", "third", "fourth", etc. (if any) in the specification, claims and drawings of the present invention are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments described here can be implemented in an order different from that shown or described here. In addition, the terms "include" or "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0022] The residual frequency offset only brings a global rotation of the phase factor during the entire combining process. Subsequent demodulation is based on the phase difference between symbols rather than the absolute phase value, completely eliminating the influence of the frequency offset. The absolute phase θ is completely cancelled out in the conjugate multiplication, ensuring that any constant phase offset cannot affect the differential result. Modern digital matched filters achieve multipath isolation by setting the correlator spacing (e.g., ≥1 / 2 chip period). As long as the timing error does not cause inter-path crosstalk, the sampling deviation only affects the symbol synchronization within each path, and the calculation of the energy weight is independent of the symbol synchronization process. Therefore, the solution of the present invention is not sensitive to frequency offset, phase offset, and sampling deviation.

[0023] For ease of understanding, the specific process of the embodiment of the present invention will be described below. Please refer to Figure 1 , the first embodiment of the signal receiving method applied to DSSS-OQPSK in the embodiment of the present invention includes:

[0024] Perform multipath separation on the received signal, and sequentially execute for each path:

[0025] a. Perform despreading processing based on the direct sequence spreading code to generate a complex symbol sequence containing phase error;

[0026] b. Perform conjugate difference operation on adjacent complex symbols to eliminate the phase error, and obtain the differential symbol after eliminating the phase error;

[0027] Combine the differential symbols after eliminating the phase error according to the received power of the path where they are located, and the received power is obtained through channel estimation (CE);

[0028] Output the combined demodulated signal.

[0029] Specifically:

[0030] 1. Perform DSSS despreading (spreading length L) on the i-th path:

[0031]

[0032] where P r represents the output after despreading, and Δ Φ represents the phase error accumulated by the residual phase offset, frequency offset, and sampling offset. Δ t represents the timing sampling deviation, which is generally small and can be ignored.

[0033] 2. Differential output

[0034] Perform conjugate multiplication on two adjacent despreading outputs of the i-th path to obtain:

[0035]

[0036] 3. Energy-based combination

[0037] The multipaths can be considered independent of each other, and for each path the power p of each path is obtained by using the estimated value of CE i , and energy-based combining is performed on N output differential symbols. The combining method can be equal-gain combining: selection combining:

[0038] Under the IEEE 802.15.4 standard (2.4 GHz frequency band), when the frequency offset reaches ±150 kHz (100 times the standard tolerance), the system bit error rate of the solution of the present invention only increases by 0.8 dB; in a DSSS system with a chip rate of 2 MHz, when allowing a symbol synchronization deviation of ±125 ns (0.25 chip period), the error of the energy weight value ≤ 3%.

[0039] The signal receiving method applied to DSSS-OQPSK in the embodiments of the present invention has been described above. Next, the differential rake receiver applied to DSSS-OQPSK in the embodiments of the present invention will be described:

[0040] A multipath separation and despreading unit is used to perform multipath separation on the received signal and sequentially execute the following operations on each path:

[0041] a. Perform despreading processing based on the direct sequence spreading code to generate a complex symbol sequence containing phase errors;

[0042] b. Perform conjugate difference operation on adjacent complex symbols to eliminate phase errors and obtain differential symbols after eliminating phase errors;

[0043] A weighted combining unit is used to combine the differential symbols after eliminating phase errors according to the received power of the path where they are located, and the received power is obtained through channel estimation (CE).

[0044] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A signal receiving method applied to DSSS-OQPSK, characterized in that It includes the following steps: Perform multipath separation on the received signal, and sequentially execute for each path: a. Perform despreading processing based on the direct sequence spread spectrum code to generate a complex symbol sequence containing phase errors; b. Perform conjugate difference operation on adjacent complex symbols to eliminate phase errors, and obtain differential symbols after eliminating phase errors; Merge the differential symbols after eliminating phase errors according to the received power of the path where they are located, and the received power is obtained through channel estimation (CE); Output the demodulated signal after merging.

2. The signal receiving method applied to DSSS-OQPSK according to claim 1, characterized in that, The formula for despreading is: Among them, the spreading length is L, P r represents the output after despreading, Δ Φ represents the residual phase offset, frequency offset, and the cumulative phase error of sampling offset. Δ t represents the timing sampling deviation, which is generally small and can be ignored.

3. A signal receiving method applied to DSSS-OQPSK according to claim 1, characterized in that, After conjugate multiplying the two despreading outputs adjacent to the i-th path, we get:

4. A signal receiving method applied to DSSS-OQPSK according to claim 1, characterized in that, The merging method is equal gain merging, and the formula for equal gain merging is:

5. A signal receiving method applied to DSSS-OQPSK according to claim 1, characterized in that The merging method is selection combining, and the formula for selection combining is:

6. A differential rake receiver applied to DSSS-OQPSK, characterized in that, The system includes: A multipath separation and despreading unit, which is used to perform multipath separation on the received signal, and sequentially execute for each path: a. Perform despreading processing based on the direct sequence spread spectrum code to generate a complex symbol sequence containing phase errors; b. Perform conjugate difference operation on adjacent complex symbols to eliminate phase errors, and obtain differential symbols after eliminating phase errors; A weighted merging unit, which is used to merge the differential symbols after eliminating phase errors according to the received power of the path where they are located, and the received power is obtained through channel estimation (CE); An output unit, which is used to output the demodulated signal after merging.

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