RANDOM PHASE MODULATION METHOD DEPENDING ON COMMUNICATION DISTANCE

Abstract

A random phase modulation method depending on a communication distance is provided. In the method, time synchronization is carried out by means of a transmitter and a receiver, a local random signal is generated, and an original signal to be sent is pre-coded according to a transmission delay and the generated local random signal, such that random phase modulation depending on a communication distance is realized, potential security brought about by positions of the transmitter and the receiver is fully utilized, a receiver at an expected distance position can receive a signal with a correct phase, and a receiver at another distance position receives a signal with a scrambled phase, thereby improving the secure communication capability of a wireless communication system in terms of the dimension of space.

Claims

1. A random phase modulation method depending on a communication distance, comprising the following steps: step 1: performing time synchronization on a transmitter and a receiver, wherein the transmitter is configured to process and send an original signal, and the receiver is configured to recover a received signal; step 2: according to a sampling rate T.sub.s agreed in advance, obtaining, by the transmitter and the receiver, a k.sup.th sampling time:
t.sub.k=t.sub.0+kT.sub.z wherein to represents an initial sampling time; step 3: generating, by the transmitter, a local random signal (t.sub.0) at the initial sampling time at the initial sampling time t.sub.0, wherein (t.sub.0) has a uniform distribution in an interval [0,2); generating, by the transmitter, a local random signal (t.sub.k) at a k.sup.th sampling time according to a local random signal (t.sub.k1) at a previous sampling time, wherein a generation method is as follows:
(t.sub.k)=(t.sub.k1)+{square root over (1.sup.2)}(t.sub.k) wherein is a constant on an interval [0,1], (t.sub.k) is a local random signal increment generated by the transmitter at the k.sup.th sampling time, and (t.sub.k) has a uniform distribution in the interval [0,2); step 4: calculating, by the transmitter, a sampling point offset $=.Math.\frac{t}{T_s}.Math.$ between the transmitter and the receiver according to a transmission delay t of the receiver, wherein represents a round-up operation; generating, by the transmitter, a precoding signal at the k.sup.th sampling time according to a local random signal (t.sub.k+) at a k+.sup.th sampling time; step 5: multiplying, by the transmitter, an original signal s.sub.k at the k.sup.th sampling time with the precoding signal .sub.k at the k.sup.th sampling time to obtain a transmitting signal x.sub.k=s.sub.k.sub.k at the k.sup.th sampling time, and sending the transmitting signal to the receiver, wherein the original signal s.sub.k represents a data signal to be sent; and step 6: estimating, by the receiver, the transmitting signal at the k.sup.th sampling time to obtain a received signal r.sub.k at the k.sup.th sampling time, generating, by the receiver, a local matched signal .sub.k=e.sup.j(t.sup.k.sup.) at the k.sup.th sampling time according to the local random signal (t.sub.k) at the k.sup.th sampling time, and multiplying, by the receiver, the received signal r.sub.k at the k.sup.th sampling time with the local matched signal .sub.k at the k.sup.th sampling time to obtain an estimation .sub.k of the original signal at the k.sup.th sampling time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a block diagram of signal processing of a transmitter according to the present invention;

[0017] FIG. 2 is a block diagram of signal processing of a receiver according to the present invention; and

[0018] FIG. 3 shows EVM performance of a system described in Embodiment 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0020] A transmitter adopts an architecture shown in FIG. 1. It is assumed that the transmitter and a receiver agree on a sampling rate T.sub.s=0.025 s in advance. An initial sampling time is t.sub.0=0. It is assumed that a distance from the transmitter to the receiver is 3 km.

[0021] Time synchronization is performed on the transmitter and the receiver.

[0022] The transmitter and the receiver obtain a k.sup.th sampling time t.sub.k=kT.sub.z=0.025 k s according to the sampling rate T.sub.s agreed in advance.

[0023] The transmitter generates a local random signal (t.sub.0) at the initial sampling time at the initial sampling time t.sub.0, where (t.sub.0) has a uniform distribution in interval [0,2). At the k.sup.th sampling time, where k=1,2,3, . . . , the transmitter generates a local random signal (t.sub.k) at the k.sup.th sampling time according to the local random signal (t.sub.k1) at the previous sampling time, where the generation method is as follows:

(t.sub.k)=(t.sub.k1)+{square root over (1.sup.2)}(t.sub.k) [0024] where =0.99, and (t.sub.k) has a uniform distribution in the interval [0,2).

[0025] The transmitter calculates a sampling point offset

[00002]$=.Math.\frac{t}{T_s}.Math.=400$

between the transmitter and the receiver according to a transmission delay t=(3 km)/c=10 s to generate a precoding signal .sub.k=e.sup.j(t.sup.k+400.sup.) at the k.sup.th sampling time, where c is a propagation speed of electromagnetic waves in space, and (t.sub.k+400) represents a local random signal at the k+400.sup.th sampling time.

[0026] The transmitter multiplies the original signal s.sub.k at the k.sup.th sampling time with the precoding signal .sub.k at the k.sup.th sampling time to obtain the transmitting signal x.sub.k=s.sub.k.sub.t at the k.sup.th sampling time, and the transmitting signal is sent to the receiver.

[0027] The receiver adopts an architecture shown in FIG. 2, the receiver estimates the transmitting signal at the k.sup.th sampling time to obtain a received signal r.sub.k at the kth sampling time. The receiver generates a local matched signal .sub.k=e.sup.j(t.sup.k.sup.) according to the local random signal (t.sub.k) at the k.sup.th sampling time. The receiver multiplies the received signal r.sub.k at the k.sup.th sampling time with the local matched signal .sub.k at the k.sup.th sampling time to obtain an estimation .sub.k of the original signal at the k.sup.th sampling time.

[0028] FIG. 3 shows a relationship between EVM performance of a system described in this embodiment and the transmission distance. It can be seen that only a receiver near an expected distance position of 3 km can receive a signal with a correct phase, and the error vector magnitude (EVM) is equal to 0%; and receivers at other positions receive signals with scrambled phases, and the EVM value is not 0, but greater than 100%.