CN105450259B - Intelligent meter data recording system multi-carrier communication module self-adaptive modulation method - Google Patents

Abstract

The invention discloses a kind of intelligent meter data recording system multi-carrier communication module self-adaptive modulation methods.This method is under the limitation of target error rate and fix power allocation, sub-carrier signal-noise ratio estimated value and multi-subcarrier signal-to-noise ratio (SNR) estimation value are obtained by the estimation of multi-carrier communication module channel gain and frame preamble data first, then the additional bit of OFDM symbol can be increased to according to signal-to-noise ratio (SNR) estimation acquisition, adaptive the distributing to of additional bit finally influences into average error rate minimum subcarrier by the increment bit error rate of subcarrier, so as to obtain the modulator approach close to optimum transmission rate, reduce the complexity of operation and be easily achieved and apply.

Description

Adaptive modulation method of multi-carrier communication module in intelligent meter reading system

technical field

The invention relates to an adaptive modulation method for a multi-carrier (OFDM, Orthogonal Frequency Division Multiplexing) communication module of an intelligent meter reading system.

Background technique

The multi-carrier communication module of the existing intelligent meter reading system has the implementation standards of G3 standard OFDM power line carrier communication technology and PRIME standard OFDM power line carrier communication technology. The PRIME standard is similar to the G3 standard, so here we take the G3 standard as an example to illustrate the existing technology. shortcoming. In the G3 standard, on the basis of meeting the requirements of transmission rate or bit error rate, each subcarrier switches between different modes, but each subcarrier adopts the same modulation method and transmission power, and some subcarriers with serious interference are turned off to resist interference. Design parameters such as modulation and coding based on the worst channel conditions. The system includes a lot of overhead to overcome the worst conditions. This is done at the expense of spectrum utilization and information transmission rate in exchange for reliability. The main disadvantages are as follows:

1. The robustness of subcarriers with relatively large noise interference will be weakened, so transmission errors are serious and transmission efficiency is low.

2. For a subcarrier with a high signal-to-noise ratio, using a modulation method with low transmission efficiency will waste bandwidth.

3. All subcarriers use the same modulation and demodulation method, which will reduce the transmission efficiency and anti-interference ability of the entire system.

Contents of the invention

The purpose of the present invention is to provide a non-iterative adaptive modulation method with an optimal transmission rate for a multi-carrier communication module of an intelligent meter reading system under the premise of a given target bit error rate (BER, Bit Error Rate) and fixed power allocation.

This intelligent meter reading system multi-carrier communication module adaptive modulation method provided by the present invention comprises the following steps:

Step 1, initialize the target bit error rate _PT , _PT is determined by the transmission performance requirements of the multi-carrier communication module, and all subcarriers are allocated with fixed power;

Step 2, calculate subcarrier signal-to-noise ratio (SNR, Signal Noise Ratio) γ _n ;

Step 3. From the subcarrier SNR γ _n , under the constraint of P _n < _PT , calculate the number of bits b _n that can be pre-allocated for each subcarrier, where b _n and P _n are the bits of each subcarrier and BER, and calculate the average bit error rate

Step 4, from the subcarrier SNR γ _n and the average bit error rate Calculate the current multi-channel SNR γ _mc and the average number of bits of subcarriers

Step 5, under the constraint of _PT , calculate the maximum average number of bits per subcarrier by γ _mc and an extra bit I that can be added to the OFDM symbol;

Step 6, when the subcarrier's Calculate the incremental bit error rate ΔP _n on this subcarrier, that is, calculate the increased bit error rate when the maximum number of bits is allocated to this subcarrier, and arrange ΔP _n in ascending order of values;

Step 7. Add 1 additional bit to the subcarrier with the lowest ΔP _n .

The beneficial effects of the present invention are: the present invention determines the additional subcarriers that can be allocated to subcarriers according to the estimated SNR of each subcarrier and the estimated SNR of multiple subcarriers under the constraints of the target bit error rate and fixed power allocation. Bits, and assign them to the subcarriers that have the least impact on the average bit error rate, so as to adaptively adjust the number of bits in each subcarrier, and obtain a modulation method close to the optimal transmission rate, which reduces the complexity of operations and is easy to implement and apply.

Description of drawings

Fig. 1 is a system structure diagram of the multi-carrier communication module of the intelligent meter reading system of the present invention.

Fig. 2 is the packet frame structure of the multi-carrier communication module of the intelligent meter reading system of the present invention.

Fig. 3 is a flow chart of the adaptive modulation method of the present invention.

Detailed ways

The power carrier module of the smart meter reading system is directly oriented to the physical medium power line that actually undertakes data transmission. It provides a physical connection for the upper layer application data to transmit the original bit stream on the power line, so the power carrier module directly faces various interferences of the power line and decay.

The present invention will be further described below in conjunction with accompanying drawing.

As shown in Figure 1, the sending end of the multi-carrier communication module of the smart meter reading system includes a forward error control encoder and an OFDM modulation module. The data to be transmitted is first subjected to crosstalk, RS coding, convolutional coding, interleaving, and then adaptive modulation and sent to do IFFT transformation. The structure of the corresponding receiving end is just opposite to that of the sending end. The received data is firstly subjected to symbol synchronization, and then FFT transformation is performed, and the channel is estimated at the same time. The data after FFT transformation is demodulated, and the multi-ary data bits are converted into binary data code streams, followed by de-interleaving, Viterbi decoding, de-crosstalk processing, and finally the transmission end data.

The frequency attenuation characteristics of low-voltage power lines determine that different subcarriers have different noise interference. Under the premise of certain bandwidth and transmission power, in order to improve the transmission capacity of the OFDM system, an adaptive modulation method is adopted in the OFDM carrier module. According to The carrier channel SNR estimation dynamically allocates bits.

As shown in FIG. 2 , the packet frame structure of the multi-carrier communication module of the intelligent meter reading system of the present invention includes a preamble, a frame control header and a data segment. The preamble sequence consists of 8 identical symbols and 1.5 inverted symbols. Use the identical 8 symbols and the channel gain estimate at the receiving end to obtain the SNR of the subcarrier, and calculate the subcarrier signal-to-noise ratio according to the following formula :

n=1,2,...,N, where ρ _n , H _n and are the signal power, channel gain estimate and noise power of the nth subcarrier, respectively, and N is the number of subcarriers used. Because the preamble sequence is known, the subcarrier signal power ρ _n is known, the channel gain H _n is obtained by channel estimation, and the noise power It is obtained by subtracting the preamble power at the receiving end from ρ _n ×|H _n | ² .

The frame control header contains important information for demodulating the data frame. Following the frame control header is a data symbol, known as the payload.

Below in conjunction with Fig. 3 illustrate this intelligent meter reading system multi-carrier communication module self-adaptive modulation method provided by the present invention, the concrete implementation steps of this method:

Step 1, initialize the target bit error rate P _T , and allocate fixed power to all subcarriers;

Step 2, calculate the subcarrier signal-to-noise ratio (SNR, SignalNoise Ratio) from the preamble data of the previous frame and the estimated channel gain value H _n :

n=1,2,...,N, where ρ _n , H _n and are the signal power, channel gain estimate and noise power of the nth subcarrier, respectively, and N is the number of subcarriers used;

Step 3, from the subcarrier signal-to-noise ratio γ _n , under the constraint of P _n < _PT , calculate the number of bits b _n that can be pre-allocated and the average bit error rate of subcarriers for each subcarrier

where b _n and P _n are bits per subcarrier and BER, respectively;

Step 4, from the subcarrier SNR γ _n and the average bit error rate Calculate the current multi-channel SNR γ _mc and the average number of bits of subcarriers

in, and are the average number of bits and the average BER of subcarriers, respectively, and γ _mc is the multi-channel signal-to-noise ratio;

Step 5, under the constraint of _PT , calculate the maximum average number of bits per subcarrier by γ _mc

Step 6, calculate the extra bits that can be added to the OFDM symbol:

Step 7, when the subcarrier's Calculate the incremental bit error rate ΔP _n on this subcarrier, that is, calculate the increased bit error rate when the subcarrier is assigned the maximum number of bits:

n=1,2,...,N, where is the bit error rate when the nth subcarrier is modulated with the maximum bit, and ΔP _n is arranged in ascending order of values.

Step 8, adding 1 additional bit to the subcarrier of the lowest ΔP _n . The method is to allocate the maximum number of bits to each lowest ΔP _n subcarrier, that is, adopt the highest order modulation allowed by the system, until all I extra bits are allocated or the maximum number of bits is allocated to the lowest ΔP _n subcarriers.

Claims (3)

1. A multi-carrier communication module self-adaptive modulation method of an intelligent meter reading system calculates extra bits which can be added to a current symbol sub-carrier through a matched formula, and finds out the sub-carrier which has the minimum influence on the average bit error rate in all sub-carriers to distribute, and is characterized in that: the adaptive modulation method of the multi-carrier communication module of the intelligent meter reading system comprises the following steps:

step 1, initializing a target bit error rate P_T，P_TAll sub-carriers are allocated with fixed power according to the requirement of the transmission performance of the multi-carrier communication module;

step 2, calculating the Signal-to-Noise Ratio (SNR) gamma of the subcarrier_n；

Step 3, the signal-to-noise ratio gamma of the sub-carrier wave_nAt P_n<P_TUnder the limitation of (2), calculating the maximum pre-allocatable bit number b for each subcarrier_nWherein b is_nAnd P_nRespectively, the Bit Error Rate (BER) of each subcarrier, and calculating the average Bit Error Rate (BER)

Step 4, the signal-to-noise ratio gamma of the sub-carrier wave_nAnd average bit error rateCalculating the current multi-channel signal-to-noise ratio gamma_mcAnd average number of bits of subcarrier

Step 5, in P_TUnder the limitation of (2), by γ_mcCalculating the maximum average number of bits per subcarrierAnd additional bits I that can be added to the OFDM symbol;

step 6, when the subcarrierCalculating the incremental bit error rate delta P on the sub-carrier_nI.e. calculating the increased error rate when the subcarrier is allocated with the maximum bit number, and calculating the delta P_nIn ascending order of value;

step 7, add I extra bits to the lowest Δ P_nThe sub-carriers of (a).

2. The adaptive modulation method for the multi-carrier communication module of the intelligent meter reading system according to claim 1, wherein the calculation of the sub-carrier signal-to-noise ratio is performed by using pilot data and a channel estimation value at a receiving end.

3. The adaptive modulation method for the multi-carrier communication module of the intelligent meter reading system according to claim 1, wherein the I extra bits are added to the lowest delta P_nFor each lowest Δ P, the subcarrier_nDistributing maximum bit number to subcarrier, i.e. adopting maximum order modulation allowed by system, until all I extra bits are distributed or lowest delta P_nThe subcarriers are allocated the maximum bits.