CN114978844A

CN114978844A - Phase cycle slip elimination method of constant envelope orthogonal frequency division multiplexing technology

Info

Publication number: CN114978844A
Application number: CN202210570049.5A
Authority: CN
Inventors: 谭佳滨; 肖悦; 但黎琳
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2022-05-24
Filing date: 2022-05-24
Publication date: 2022-08-30
Anticipated expiration: 2042-05-24
Also published as: CN114978844B

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a phase cycle slip elimination method of a constant-envelope orthogonal frequency division multiplexing technology. In the method provided by the invention, the cycle slip detection and the windowing correction are carried out on the received phase signals, so that the influence of the cycle slip on the whole signals is reduced. Compared with the scheme of directly using the original phase for detection, the scheme provided by the invention can provide better performance gain.

Description

Phase cycle slip elimination method of constant envelope orthogonal frequency division multiplexing technology

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a phase cycle slip elimination method of a constant-envelope orthogonal frequency division multiplexing technology.

Background

Recently, a new multi-carrier modulation technique, a Constant Envelope Orthogonal Frequency Division Multiplexing (CE-OFDM), has been proposed, and the key idea is to modulate an OFDM signal onto a carrier phase for transmission. By this operation, the signal can maintain a Peak to Average Power Ratio (PAPR) of 0 dB. Therefore, the technology is expected to be used in various low PAPR scenarios.

However, since the phase is only valid in the range of [ - π, π ], a phase unwrapping (unwrap) is required to obtain continuous phase, which results in cycle slip problems for CE-OFDM signals.

Disclosure of Invention

Aiming at the problems, the invention improves the overall error code performance of the CE-OFDM system by repairing the received phase signals.

For ease of understanding, the modified soft decision scheme employed by the present invention is illustrated as follows:

the transmitted baseband CE-OFDM complex signal may be denoted as s _t ＝e ^j2πhCx Wherein 2 pi h is a modulation index,

for a normalized constant, N is the number of OFDM-modulated subcarriers, N _c For the effective number of subcarriers (i.e. the number of subcarriers actually used),

for the transmitted modulation symbol variance, for M-QAM modulation,

and x is the OFDM modulated signal. For ease of understanding, only the gaussian channel is considered here, and the received signal can be denoted as s _r ＝e ^j2πhCx + w, where w is gaussian noise.

The technical scheme of the invention is as follows:

a phase cycle slip elimination method of constant envelope orthogonal frequency division multiplexing technology comprises the following steps:

s1, acquiring the phase phi of the received signal to be equal to the angle S _r To phi n]N is more than or equal to 0 and less than or equal to l-1, k belongs to Z, Z represents an integer set, and l is the length of the whole signal. To obtain

So that the phase difference is continuous

S2, using a window pair with size S

Calculating the average value to obtain the offset O closest to the average value ₀ 2 π k, k ∈ Z. Subtracting the entire phase signalThe offset amount

Initializing i ═ S.

S3, if i is more than or equal to l-S, go to S6.

Otherwise, ask for

d ₁ ＝max(|φ[i]-φ[i-1]|,|φ[i+1]-φ[i]|). If d is ₀ >1.2 pi and d ₁ >π, go to S4; otherwise, go to S5.

S4, calculating

Mean value, obtaining the offset O closest to the mean value _i 2 pi k, k e Z. Subtracting the offset from the subsequent phase signal

All phases after index i are indicated. Let i equal i + S, go to S3.

S5, turn S3 when i is equal to i + 1.

S6, use

And performing final symbol detection.

The method has the advantages that in the method, cycle slip detection and windowing correction are carried out on the originally received phase signals, so that the influence of the cycle slip on the whole signals is reduced. Compared with the scheme of directly using the original phase for detection, the scheme provided by the invention can provide better performance gain.

Drawings

FIG. 1 is a flow chart of an algorithm;

fig. 2 is a schematic diagram showing the comparison of the bit error rate performance of the original phase detection and the corrected phase detection when the number of OFDM points is 512, the number of effective subcarriers is 128, the modulation index is 1, and the window size S is 20.

Detailed Description

The technical scheme of the invention is described in detail in the following with reference to the accompanying drawings and embodiments:

the technical scheme of the invention mainly lies in the proposed cycle slip detection and correction method, and the specific derivation process is as follows:

for the received phase signal phi ═ s _r Since the transmitted phase signal may exceed-pi, pi]So as to be aligned with n]N is more than or equal to 0 and less than or equal to l-1, and k belongs to Z

So that the phase difference is continuous

A continuous phase is obtained. However, this operation may lead to the occurrence of phase cycle slip. The specific expression in CE-OFDM demodulation is as follows:

there is an offset of 2 π k, k ∈ Z from the true transmit phase and this offset still exists in the subsequent phase.

Also, by testing, we found that when a cycle jump occurred, for

d ₁ ＝max(|φ[i]-φ[i-1]|,|φ[i+1]-φ[i]|)，d ₀ >1.2 pi and d ₁ >The probability of pi occurrence is large.

Thus, initially, a window of size S may be used, for

Calculating the average value to obtain the offset O closest to the average value ₀ 2 pi k, k e Z. The offset is then subtracted from the entire phase signal

And (5) finishing the initialization process of the algorithm by taking i as S.

Thereafter, traversal can be made

And phi i],1≤i<l-S-1. Observe whether d is ₀ >1.2 pi and d ₁ >Pi, if satisfied then use a window of size S, get

And obtaining an offset O closest to the mean _i 2 pi k, k e Z. Subtracting the offset from the subsequent phase signal

All phases after index i are indicated. Then, let i be i + S, and continue the subsequent traversal.

After traversal is complete, the corrected phase can be used

The signal is detected.

Examples

In this example, the phase signal length l is 512, the window size is 20, and the modulation scheme is QPSK.

S1, obtaining the phase phi of the receiving signal ═ S _r To phi n]N is more than or equal to 0 and less than or equal to l-1, k belongs to Z, and Z represents an integer set. To obtain

So that the phase difference is continuous

S2, using a window pair with size S-20

Calculating the average value to obtain the offset O closest to the average value ₀ 2 pi k, k e Z. E.g., 1.8 π, then its closest O ₀ 2 pi. Subtracting the offset from the entire phase signal

InitialChange i to 20.

S3, if i is more than or equal to l-S, go to S6.

Otherwise, ask for

S4, calculating

All phases following the index i are indicated, for example when i equals 2,

to represent

All the points of (a). Let i be i + S, go to S3.

S5, turn S3 when i is equal to i + 1.

S6, use

And performing final symbol detection to obtain a QPSK signal.

Claims

1. A method for eliminating phase cycle slip in constant envelope orthogonal frequency division multiplexing technology is characterized by comprising the following steps:

s1, acquiring the phase phi of the received signal to be equal to the angle S _r ，s _r To receive signals, order

Z represents an integer set, l is the length of the whole signal, and the result is

So that the phase difference is continuous

S2, using a window pair with the size of S

Calculating the average value to obtain the offset O closest to the average value ₀ 2 π k, k ∈ Z. Subtracting the offset from the entire phase signal

Initializing i ═ S;

s3, if it is judged that i is more than or equal to l-S, if yes, the operation goes to S6,

otherwise, ask for

If d is ₀ >1.2 pi and d ₁ >π, go to S4; otherwise, go to S5;

s4, calculating

Mean value, obtaining the offset O closest to the mean value _i 2 pi k, k e Z, subtracting the offset from the subsequent phase signal

Denote all phases after subscript i, let i ═ i + S, go to S3;

s5, making i equal to i +1, and turning to S3;

s6, use of

The signal is detected.