CN102710404A - Transmission method for low transmitting power and single carrier-frequency division multiplexing access system - Google Patents

Abstract

The invention discloses a transmission method for a low transmitting power and single carrier-frequency division multiplexing access system. Under the basic background that a demodulated reference signal is from a finite set, a method for finding the demodulated reference signal with smaller PAPR (Peak to Average Power Ratio) by iterating is provided. According to the method, for each system composition, smaller PAPR is found by calculating and is formed into a combined demodulated reference signal form. Compared with the prior method, the method has the advantages that the disadvantages of the system caused by the demodulated reference signal with high PAPR are effectively overcome; and once the form is generated, the form can be reused and further the complexity is low. According to the transmission method disclosed by the invention, the problem that a demodulated detection signal with high PAPR is easily distorted when passing through an amplifier is effective solved; and the PAPR is reduced while no error rate of the system is lost.

Description

Transmission method of low transmitting power single carrier frequency division multiple access system

Technical Field

The invention belongs to the technical field of mobile communication, and particularly relates to a Carrier Aggregation (CA) technology of LTE-A.

Background

In the evolution process from LTE to LTE-Advanced system, the requirement of wider spectrum will beBecoming an important factor influencing evolution, for this reason, 3GPP proposes a carrier aggregation technology as one of the key technologies of the LTE-Advanced system. The basic purpose is to aggregate a plurality of relatively narrow-band carriers into a wider spectrum, thereby meeting the requirements of LTE-Advanced. In the LTE-a system, each Component Carrier (CC) has a separate demodulation reference signal (SRS), but in the case of multiple CCs, superposition of different SRS increases the Peak-to-Average Power Ratio (PAPR) of the transmitted signal. The PAPR here is formulated as:

wherein x is_nRepresents the output signal obtained after IFFT operation, max [ ·]Represents the maximum value, E [ ·]The average value is shown. When a high peak signal enters a power amplifier saturation region at a system transmitting end, great in-band distortion and out-of-band radiation are generated, signal distortion and adjacent-band interference are caused, and system performance is deteriorated. For distortion-free transmission of SC-FDMA signals, a large linear range is required for the transmitting end, which increases the cost of system design and limits the application range.

Many methods have been proposed for how to reduce the PAPR of a signal, but there are few methods on how to reduce the PAPR of a demodulation reference signal. LTE Rel-8 presents two approaches to reducing cubic coefficients: one is to use different sequence sets for different CCs, and the other is to use different cyclic shifts for different CCs. The literature does not give a specific reference signal selection scheme based on low PAPR. The details are shown in 3GPP R1-100308, NEC Group, NTT DOCOMO, "CM reduction of ULRS for carrier aggregation in LTE-A," 2010.

Disclosure of Invention

In order to overcome the above disadvantages of the prior art, the present invention provides a transmission method of a low transmission power single carrier frequency division multiple access system, which selects a combined demodulation reference signal from a table by finding an optimal demodulation reference signal and tabulating the optimal demodulation reference signal, wherein the PAPR of the selected demodulation reference signal is small and the performance of the system is not reduced.

The technical scheme adopted by the invention for solving the technical problems is as follows: a transmission method of a low transmission power single carrier frequency division multiple access system comprises the following steps:

(1) the method comprises the steps that information sending bits of a user are firstly subjected to signal coding, and then PSK or QAM modulation is carried out to form modulation symbols;

(2) performing DFT precoding on the modulation symbols;

(3) selecting a demodulation reference signal: for a first subframe signal, firstly, searching an optimal demodulation reference signal, making a table, and selecting a combined demodulation reference signal from the table; for the subsequent subframe signals, directly selecting from the table;

(4) mapping each CC precoding signal and the selected combined demodulation reference signal on a subcarrier used by a user, and aggregating all mapped member carriers;

(5) performing IFFT transformation on the signals aggregated by the CC;

(6) and adding a cyclic prefix to generate a transmitting signal.

Compared with the prior art, the invention has the following positive effects: by the basic background that the demodulation reference signal comes from a limited set, a method for iteratively searching the demodulation reference signal with a smaller PAPR is provided, and the method is formed aiming at each system, and the smaller PAPR is searched through calculation and is made into a combined demodulation reference signal table. Compared with the existing method, the method not only effectively solves the disadvantages brought by the demodulation reference signal with high PAPR to the system, but also can repeatedly use the table once being generated, thereby having low complexity. The invention effectively solves the problem that the demodulation detection signal with high PAPR is easy to distort when passing through the amplifier, and reduces the PAPR while ensuring that the error rate of the system is not lost.

Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a flow chart of the method of the present invention;

FIG. 2 is a schematic diagram of a method for selecting a demodulation reference signal;

FIG. 3 is a schematic diagram of another method for selecting a demodulation reference signal;

fig. 4 is a diagram showing simulation results.

Detailed Description

Before setting forth the detailed description, the terms used therein and the theorem used therein are first introduced:

the LTE uplink physical layer multiple access scheme is SC-FDMA and supports frequency division duplex and time division duplex modes. In the radio frame structure based on frequency division duplex, the duration of one radio frame is 10ms, and the radio frame structure is composed of 10 subframes, wherein each subframe comprises two time slots. The signal transmitted in each time slot being composed of successive signals in the frequency domain

Continuous in subcarrier and time domain

A Resource Grid (RG) consisting of SC-FDMA symbols.

The value of (c) is determined by the system bandwidth. One Resource Block (RB) consists ofA single SC-FDMA symbol and

the sub-carriers constitute, under a normal cyclic prefix,

for the LTE system under the conventional cyclic prefix, in the time domain, the 4 th SC-FDMA symbol is a reference signal, and in the frequency domain, the reference signal adopts a centralized pilot frequency placement mode, and the frequency bandwidth of the reference signal is completely the same as that of the data symbols.

The expression of the alternative demodulation reference signal is:

<math> <mrow> <msubsup> <mi>r</mi> <mrow> <mi>u</mi> <mo>,</mo> <mi>v</mi> </mrow> <mrow> <mo>(</mo> <mi>&alpha;</mi> <mo>)</mo> </mrow> </msubsup> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <msup> <mi>e</mi> <mi>j&alpha;n</mi> </msup> <msub> <mover> <mi>r</mi> <mo>&OverBar;</mo> </mover> <mrow> <mi>u</mi> <mo>,</mo> <mi>v</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> <math> <mrow> <mn>0</mn> <mo>&le;</mo> <mi>n</mi> <mo>&lt;</mo> <msubsup> <mi>M</mi> <mi>sc</mi> <mi>RS</mi> </msubsup> </mrow> </math>

whereinFor the length of the demodulation reference signal, α is the cyclic shift value

α=2πN_CS/12

$N_{\mathrm{CS}}=(n_{\mathrm{DMRS}}^{\left(1\right)}+n_{\mathrm{DMRS}}^{\left(2\right)}+n_{\mathrm{PRS}}\left(n_s\right))\mathrm{mod}12$

In a radio frame, n_s=0,1,...,19；Is configured by the parameters of the higher layer,

configured by uplink scheduling information, n_PRS(n_s) Generating by a pseudo-random generator:

each base Sequence is decomposed into 30 Sequence Groups (SG), u ∈ {0, 1.. multidot., 29} is the Group number, v is the base Sequence number in an SG, each Group contains a base Sequence number of lengthOr two lengths of

The base sequence of (1).

When the number of allocated resource blocks is 1 or 2, i.e. the length of the reference signal is 12 or 24, the base sequence

Computer Generated Sequences (CG Sequences) are used.

And when the number of the allocated resource blocks is more than or equal to 3, namely the length of the reference signal is more than or equal to 36, the base sequence adopts a Zadoff-Chu sequence. Zadoff-Chu sequences

Produced by the formula:

<math> <mrow> <msub> <mover> <mi>r</mi> <mo>&OverBar;</mo> </mover> <mrow> <mi>u</mi> <mo>,</mo> <mi>v</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>x</mi> <mi>q</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mi>mod</mi> <msubsup> <mi>N</mi> <mi>ZC</mi> <mi>RS</mi> </msubsup> <mo>)</mo> </mrow> <mo>,</mo> <mn>0</mn> <mo>&le;</mo> <mi>n</mi> <mo>&lt;</mo> <msubsup> <mi>M</mi> <mi>sc</mi> <mi>RS</mi> </msubsup> </mrow> </math>

<math> <mrow> <msub> <mi>x</mi> <mi>q</mi> </msub> <mrow> <mo>(</mo> <mi>m</mi> <mo>)</mo> </mrow> <mo>=</mo> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mi>j</mi> <mfrac> <mrow> <mi>&pi;qm</mi> <mrow> <mo>(</mo> <mi>m</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> <msubsup> <mi>N</mi> <mi>ZC</mi> <mi>RS</mi> </msubsup> </mfrac> </mrow> </msup> <mo>,</mo> </mrow> </math> <math> <mrow> <mn>0</mn> <mo>&le;</mo> <mi>m</mi> <mo>&le;</mo> <msubsup> <mi>N</mi> <mi>ZC</mi> <mi>RS</mi> </msubsup> <mo>-</mo> <mn>1</mn> </mrow> </math>

wherein,

is the largest prime number smaller than the length of the reference signal, q is determined by the following equation:

<math> <mrow> <mover> <mi>q</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <msubsup> <mi>N</mi> <mi>ZC</mi> <mi>RS</mi> </msubsup> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mi>u</mi> <mo>+</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>/</mo> <mn>31</mn> </mrow> </math>

as shown in fig. 1, a transmission method of a low transmit power single carrier frequency division multiple access system includes the following steps:

(1) coding, PSK&QAM modulatorAnd (5) preparing. The transmitted information bits of the user are first signal-coded and then PSK or QAM modulated to form modulation symbols. Given the example of K CCs, the input bits are converted into a matrix of J × K, J ═ log₂(R)+log₂(M_ary) R is coding efficiency, M_aryIs the modulation order.

(2) And performing L-point DFT precoding on the modulation symbols.

<math> <mrow> <msub> <mi>X</mi> <mi>m</mi> </msub> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>L</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msub> <mi>x</mi> <mi>n</mi> </msub> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mi>j</mi> <mfrac> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> <mi>L</mi> </mfrac> <mi>mn</mi> </mrow> </msup> <mo>,</mo> </mrow> </math> for m=0,1,…,L-1

(3) Selecting a demodulation reference signal: for the first sub-frame signal, the best demodulation reference signal is firstly found and made into a table, and the combined demodulation reference signal is selected from the table. For the subsequent subframe signals, the selection is made directly from the table.

The method for finding the optimal demodulation reference signal comprises the following two methods:

the first method is to calculate the PAPRs of all combined demodulation reference signals and select M combinations with the minimum PAPR. As shown in fig. 2, the method comprises the following steps:

assume that there are a total of K CCs in a system, and each CC has Q candidate demodulation reference signals.

Step 11, calculate all of the K CCsPAPR of combined demodulation reference signal (SRS), with G = Q^KThe seed combinations are ordered from small to large.

And step 12, storing all the combined demodulation reference signals to form a table, directly calling data from the table when the system structure and the parameters are not changed, and forming a new table according to the step 11 if the system structure and the parameters are changed so as to be convenient for standby.

And secondly, searching the next demodulation reference signal according to the previous demodulation reference signal. As shown in fig. 3, the method comprises the following steps:

assume that there are a total of K CCs in a system, and each CC has Q candidate demodulation reference signals.

Step 21, calculating PAPRs of Q alternative demodulation reference signals of the first CC, and selecting m of the PAPRs₁Using the demodulation reference signals with smaller PAPR as candidate demodulation reference signals of a first CC;

step 22, knowing m of the first CC₁Based on the candidate demodulation reference signals, calculating the PAPRs of Q candidate demodulation reference signals of the second CC aiming at each candidate demodulation reference signal, and selecting m from the PAPRs₂The smaller PAPR demodulation reference signal. In combination with the selection of two CCs, there is now a total of m₁*m₂And combining the demodulation reference signals.

Step 23, for the k-th CC, m of the first (k-1) CC is known₁*m₂……*m_k-1Based on the combined demodulation reference signals, calculating the PAPRs of Q alternative demodulation reference signals of the kth CC aiming at each combination, and selecting m from the PAPRs_kThe smaller PAPR demodulation reference signal. In combination with the selection of k CCs, there is now a total of m₁*m₂……*m_k-1*m_kAnd combining the demodulation reference signals.

And 24, repeating the step 23 until all CCs are traversed.

And step 25, storing all the combined demodulation reference signals to form a table, and directly calling data from the table when the system structure and the parameters are not changed, wherein if the system structure and the parameters are changed, a new table needs to be formed according to the steps 21 to 25 so as to be convenient for standby.

(4) The precoded signal and the selected combined demodulation reference signal are mapped on the subcarriers used by the user for each CC. And all CCs that complete the mapping are aggregated.

(5) And performing IFFT transformation on the carrier aggregated signals.

(6) Cyclic Prefix (CP) is added to generate a transmission signal.

In order to verify the correctness of the method provided by the invention, the simulation environment is that in a clustered-DFT-S-OFDM system, 2 CCs are arranged and the distance between the two CCs is 11RB, each CC has 2 clusters, and the sizes of the CCs are 2RB and 3RB respectively. As can be seen from fig. 4, in the case that the number of candidate combined demodulation reference signals is the same, the PAPR of the demodulation reference signal of the method one is smaller than that of the method two, and the PAPR of the two methods decreases as the number of candidate combined demodulation reference signals decreases.

Claims (3)

1. A transmission method of a low transmission power single carrier frequency division multiple access system is characterized in that: the method comprises the following steps:

(1) the method comprises the steps that information sending bits of a user are firstly subjected to signal coding, and then PSK or QAM modulation is carried out to form modulation symbols;

(2) performing DFT precoding on the modulation symbols;

(3) selecting a demodulation reference signal: for a first subframe signal, firstly, searching an optimal demodulation reference signal, making a table, and selecting a combined demodulation reference signal from the table; for the subsequent subframe signals, directly selecting from the table;

(4) mapping each member carrier pre-coding signal and the selected combined demodulation reference signal on a subcarrier used by a user, and aggregating all the member carriers which are mapped;

(5) performing IFFT transformation on the signals aggregated by the component carriers;

(6) and adding a cyclic prefix to generate a transmitting signal.

2. The transmission method of a low transmit power single-carrier frequency division multiple access system according to claim 1, wherein: the method for searching the optimal demodulation reference signal in the step (3) comprises the following steps: calculating the PAPRs of all combined demodulation reference signals, and selecting M combinations with the minimum PAPR from the PAPRs, wherein the specific steps are as follows:

assuming that there are K component carriers in a system, each component carrier has Q candidate demodulation reference signals,

step 11, calculating PAPR of all combined demodulation sounding reference signals of K component carriers, wherein the PAPR is G = Q^KSeed combinations are sequentially ordered from small to large;

step 12, storing all the combined demodulation reference signals, making a table, and directly calling data from the table when the system structure and parameters are unchanged; when the system structure and parameters are changed, a new table is formed for standby according to steps 11 to 12.

3. The transmission method of a low transmit power single-carrier frequency division multiple access system according to claim 1, wherein: the method for searching the optimal demodulation reference signal in the step (3) comprises the following steps: searching the next demodulation reference signal according to the previous demodulation reference signal, which comprises the following steps:

assuming that a system has K member carriers in total, and each member carrier has Q alternative demodulation reference signals;

step 21, calculating PAPRs of Q candidate demodulation reference signals of the first member carrier, and selecting m of the PAPRs₁Demodulation reference signal with smaller PAPRThe number is used as a candidate demodulation reference signal of the first member carrier;

step 22, knowing m of the first component carrier₁Based on the candidate demodulation reference signals, calculating the PAPRs of the Q candidate demodulation reference signals of the second member carrier aiming at each candidate demodulation reference signal, and selecting m from the PAPRs₂A demodulation reference signal with a smaller PAPR; combining the selection of two component carriers, and the total is m₁*m₂A combined demodulation reference signal;

step 23, for the k component carrier, m of the first k-1 component carriers is known₁*m₂……*m_k-1Based on the combined demodulation reference signals, calculating the PAPR of Q alternative demodulation reference signals of the kth member carrier aiming at each combination, and selecting m from the PAPR_kThe demodulation reference signals with smaller PAPR are combined with the selection of k component carriers, and the total number of the demodulation reference signals is m₁*m₂……*m_k-1*m_kA combined demodulation reference signal;

step 24, repeating step 23 until all the member carriers are traversed;

step 25, storing all the combined demodulation reference signals, making a table, and directly calling data from the table when the system structure and parameters are unchanged; when the system configuration and parameters are changed, a new table is formed according to steps 21 to 25 for standby.

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