CN114978844B

CN114978844B - Phase cycle slip eliminating method for normal envelope orthogonal frequency division multiplexing technology

Info

Publication number: CN114978844B
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: 2023-05-26
Anticipated expiration: 2042-05-24
Also published as: CN114978844A

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 influence of cycle slip on the whole signal is reduced by performing cycle slip detection and windowing correction on the received phase signal. Compared with the method for detecting by directly using the original phase, the method provided by the invention can provide better performance gain.

Description

Phase cycle slip eliminating method for normal 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, chang Baolao orthogonal frequency division multiplexing (Constant Envelope Orthogonal Frequency Division Multiplexing, CE-OFDM), has been proposed, the key idea of which is to modulate OFDM signals onto carrier phases for transmission. By this operation, the signal can maintain a peak-to-average ratio (Peak to Average Power Ratio, PAPR) of 0 dB. Therefore, the technique is expected to be used for various low PAPR scenes.

However, since the phase is only valid in the range of [ -pi, pi ], a phase unwrapping (unwrap) is required to obtain a continuous phase, which however causes a cycle slip problem for the CE-OFDM signal.

Disclosure of Invention

The invention aims at the problems, and 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 described as follows:

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

for normalization constant, N is the number of subcarriers of OFDM modulation, N _c Is the effective number of sub-carriers (i.e. the number of sub-carriers actually used),/and the like>

For the transmitted modulation symbol variance,/for M-QAM modulation>

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

The technical scheme of the invention is as follows:

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

s1, acquiring a phase phi= & lt S of a received signal _r For phi [ n ]]2 kpi, n is more than or equal to 0 and less than or equal to l-1, k epsilon Z, Z represents an integer set, and l is the length of the whole signal. Obtaining

So that the continuous phase difference ∈>

S2, using a window pair with the size of S

Averaging to obtain the closest offset O of the average ₀ =2pi.k, k∈z. Subtracting the offset from the whole phase signal>

Initializing i=s.

S3, if i is not less than l-S, turning to S6.

Otherwise, calculate

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

S4, calculating

Average value, obtain the closest offset O of the average value _i =2pi.k, k∈z. Subtracting the offset from the subsequent phase signal>

Indicating all phases following the index i. Let i=i+s, go to S3./>

S5, let i=i+1, go to S3.

S6, use

And performing final symbol detection.

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

Drawings

FIG. 1 is a flow chart of an algorithm;

fig. 2 is a graph showing bit error rate performance comparison using original phase and modified phase detection for a window size s=20 with an OFDM point number of 512, an effective number of subcarriers of 128, and a modulation index of 1.

Detailed Description

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

the technical scheme of the invention mainly aims at providing a cycle slip detection and correction method, which comprises the following specific deduction processes:

for the accepted phase signal phi= angle s _r Since the transmitted phase signal may exceed [ -pi, pi]Thus can be applied to phi [ n ]]N is more than or equal to 0 and less than or equal to l-1, and k is E Z to obtain

So that the continuous phase difference ∈>

A continuous phase is obtained. However, this operation may lead to the occurrence of phase jumps. The specific implementation is in CE-OFDM demodulation: />

There is an offset of 2pi k, k e Z from the true transmit phase, and this offset still exists in the subsequent phase.

Meanwhile, through testing, we found that when cycle slip occurs, 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

Averaging to obtain the closest offset O of the average ₀ =2pi.k, k∈z. The whole phase signal is then subtracted by the offset +.>

Let i=s, the initialization process of the algorithm is completed.

Thereafter, it can be traversed

And phi [ i ]],1≤i<l-S-1. Observe whether or not d ₀ >1.2 pi and d ₁ >If it is satisfied, a window of size S is used, resulting in +.>

And obtain the offset O closest to the average _i =2pi.k, k∈z. Subtracting the offset from the subsequent phase signal>

Indicating all phases following the index i. Then let i=i+s, the subsequent traversal is continued.

After the traversal is completed, the corrected phase can be used

The signal is detected.

Examples

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

S1, acquiring a phase phi= & lt S of a received signal _r For phi [ n ]]2 kpi, n is more than or equal to 0 and less than or equal to l-1, k is E Z, and Z represents an integer set. Obtaining

So that the continuous phase difference ∈>

S2 using a window pair of size s=20

Averaging to obtain the closest offset O of the average ₀ =2pi.k, k∈z. For example, when the average value is 1.8pi, then the nearest O ₀ =2pi. Subtracting the offset from the whole phase signal>

Initializing i=20.

S3, if i is not less than l-S, turning to S6.

Otherwise, calculate

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

S4, calculating

Indicating all phases after index i, e.g. i=2,/for example>

Representation of

Is a single point of the system. Let i=i+s, go to S3.

S5, let i=i+1, go to S3.

S6, use

And performing final symbol detection to obtain QPSK signals. />

Claims

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

s1, acquiring a phase phi= & lt S of a received signal _r ，s _r For receiving signals, let

Z represents an integer set, l is the length of the whole signal, resulting in +.>

So that the continuous phase difference ∈>

S2, using a window pair with the size of S

Averaging to obtain the closest offset O of the average ₀ =2pi k, k e Z, subtracting the offset from the whole phase signal +.>

Initializing i=s;

s3, if the i is not less than l-S, judging whether the i is not less than l-S, if so, turning to S6,

otherwise, calculate

If d ₀ >1.2 pi and d ₁ >Pi, turning to S4; otherwise, go to S5;

s4, calculating

Average value, obtain the closest offset O of the average value _i =2pi k, k e Z, subtracting the offset from the subsequent phase signal>

Indicating all phases following the subscript i, let i=i+s, go to S3;

s5, letting i=i+1, turning to S3;

s6, using the obtained

The signal is detected. />