CN100386976C

CN100386976C - Power Control Method in Frequency Selective Single Carrier Block Transmission System

Info

Publication number: CN100386976C
Application number: CNB2005100423153A
Authority: CN
Inventors: 杜岩; 袁静; 李剑飞; 宫良
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2005-01-11
Filing date: 2005-01-11
Publication date: 2008-05-07
Anticipated expiration: 2025-01-11
Also published as: CN1645762A

Abstract

The present invention provides a power control method in a frequency-selective single-carrier block transmission system, which includes the following steps: (1) After the two parties establish communication, the receiving end calculates the bit error rate according to the modulation mode and the required system performance. Calculate the corresponding SNR after equalization, that is, the ratio of the signal power after equalization to the noise power; (2) The receiving end selects the available sub-channels according to the obtained channel state information, and calculates the SNR after equalization when the SNR is guaranteed. The required receiving signal-to-noise ratio, and then calculate the signal power required by the sending end through the receiving signal-to-noise ratio and link attenuation, which is called the power control information _PT of the sending signal, and is transmitted to the sending end through the feedback channel; (3 ) The sending end adjusts the sending power and sends the signal according to the received power control information and sub-channel label information. The invention changes the power of the sending signal according to the quality of the channel state, further improving the power utilization rate.

Description

Power Control Method in Frequency Selective Single Carrier Block Transmission System

(一)技术领域 (1) Technical field

本发明涉及宽带数字通信传输方法。属于宽带无线通信技术领域。The invention relates to a broadband digital communication transmission method. It belongs to the technical field of broadband wireless communication.

(二)背景技术 (2) Background technology

通信技术在最近几十年，特别是二十世纪九十年代以来得到了长足发展，对人们日常生活和国民经济的发展产生了深远的影响。而未来通信技术正朝着宽带高速的方向发展，因此许多宽带数字传输技术受到广泛的关注，正交频分复用(以下简称OFDM：Orthogonal FrequencyDivision Multiplexing)和频域均衡的单载波(以下简称SC-FDE：Single Carrier withFrequency Domain Equalization)就是两种被人们重视的宽带数字传输技术，它们都属于分块传输技术，而目前OFDM受关注的程度要远远超过SC-FDE，并且在多种标准中成为支撑技术，例如：无线局域网(WLAN：Wireless Local Area Network)中的IEEE802.11a、欧洲电信标准化协会(ETSI：European Telecommunication Standard Institute)的HiperLAN/2，无线城域网(WMAN：Wireless Metropolitan Area Network)中的IEEE802.16；有线数据传输中的各种高速数字用户线(xDSL：Digital Subscriber Line)都是基于OFDM技术的标准。SC-FDE并没有被这些标准采用，只是在IEEE802.16中与OFDM共同建议为物理层传输技术。Communication technology has developed rapidly in recent decades, especially since the 1990s, and has had a profound impact on people's daily life and the development of the national economy. The future communication technology is developing in the direction of broadband and high speed, so many broadband digital transmission technologies have received extensive attention, such as Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM: Orthogonal Frequency Division Multiplexing) and frequency domain balanced single -FDE: Single Carrier with Frequency Domain Equalization) are two broadband digital transmission technologies that are valued by people. Become a supporting technology, such as: IEEE802.11a in Wireless Local Area Network (WLAN: Wireless Local Area Network), HiperLAN/2 of European Telecommunications Standards Institute (ETSI: European Telecommunication Standard Institute), Wireless Metropolitan Area Network (WMAN: Wireless Metropolitan Area Network) ) in IEEE802.16; various high-speed digital subscriber lines (xDSL: Digital Subscriber Line) in wired data transmission are all standards based on OFDM technology. SC-FDE has not been adopted by these standards, but it is jointly proposed as a physical layer transmission technology together with OFDM in IEEE802.16.

OFDM是一种多载波传输技术，它用N个子载波把整个宽带信道分割成N个并行的相互正交的窄带子信道。OFDM系统有许多引人注目的优点：1.非常高的频谱效率；2.实现比较简单；3.抗多径干扰能力和抗衰落能力强；4.可以利用信道状态信息(即自适应OFDM技术)进一步提高频谱效率等等。OFDM is a multi-carrier transmission technology, which uses N subcarriers to divide the entire wideband channel into N parallel narrowband subchannels that are orthogonal to each other. The OFDM system has many compelling advantages: 1. Very high spectral efficiency; 2. It is relatively simple to implement; 3. It has strong anti-multipath interference and anti-fading capabilities; 4. It can use channel state information (that is, adaptive OFDM technology ) to further improve the spectral efficiency and so on.

自适应OFDM技术可以利用信道状态信息，使信号发送功率随信道状况的变化而改变，即在传码率一定，并满足一定误码率要求情况下，使发射总功率最小，从而实现功率控制，尽量减少发送功率，提高功率利用率。Adaptive OFDM technology can use channel state information to make the signal transmission power change with the change of channel conditions, that is, when the code rate is constant and meets a certain bit error rate requirement, the total transmission power is minimized, thereby realizing power control. Minimize transmission power and improve power utilization.

正是这些优点使得OFDM成为近十年来的研究热点，以致被认为是未来通信，特别是宽带无线通信的支撑技术。但OFDM系统自身的许多缺点，特别是它的峰值平均功率比(简称PAPR：Peakto Average Power Ratio)过大，限制着它的实用步伐，而现有SC-FDE具有OFDM上述除第4点以外的所有优点，并且不存在OFDM的PAPR问题，性能和效率跟OFDM基本相当。它是人们在研究OFDM的基础上发展而来，这种SC-FDE系统跟OFDM一样采取分块传输，并且采用CP(若采用零填充(简称ZP：Zero Padding)方式，而将每帧拖尾叠加到该帧的前面，则与CP效果相同)，这样就可以把信号与信道脉冲响应的线性卷积转化为循环卷积，并且消除了多径引起的帧间干扰。并且在接收端采用简单的频域均衡技术就可以消除符号间干扰，例如：迫零(简称ZF：Zero Forcing)均衡和最小均方误差(简称MMSE：Minimum Mean Square Error)均衡。It is these advantages that make OFDM a research hotspot in the past ten years, so that it is considered as the supporting technology of future communication, especially broadband wireless communication. However, many shortcomings of the OFDM system itself, especially its peak-to-average power ratio (PAPR: Peakto Average Power Ratio) is too large, which limits its practical pace, and the existing SC-FDE has the above-mentioned OFDM except point 4 All advantages, and there is no PAPR problem of OFDM, the performance and efficiency are basically equivalent to OFDM. It is developed on the basis of people's research on OFDM. This SC-FDE system adopts block transmission like OFDM, and uses CP (if zero padding (ZP: Zero Padding for short) is used, each frame is tailed. Superimposed on the front of the frame, it has the same effect as CP), so that the linear convolution of the signal and the channel impulse response can be converted into circular convolution, and the inter-frame interference caused by multipath can be eliminated. And the intersymbol interference can be eliminated by adopting simple frequency domain equalization technology at the receiving end, such as: zero-forcing (ZF: Zero Forcing) equalization and minimum mean square error (MMSE: Minimum Mean Square Error) equalization.

SC-FDE系统跟OFDM相比，不存在PAPR问题。而PAPR问题是OFDM系统本身难以用低代价(频谱效率和功率效率)方式解决的问题。因此SC-FDE技术目前受到越来越多的重视。下面简单介绍一下传统SC-FDE系统的数学模型。Compared with OFDM, SC-FDE system does not have PAPR problem. The PAPR problem is a problem that the OFDM system itself is difficult to solve in a low-cost (spectrum efficiency and power efficiency) way. Therefore, SC-FDE technology is receiving more and more attention at present. The following briefly introduces the mathematical model of the traditional SC-FDE system.

SC-FDE系统在发送端发送的一帧时域信号为s(n)，(n＝0，1，…，N-1)，通过时变多径信道，信道的脉冲响应为h(n)，(n＝0，1，…L-1)，信号传输过程中受到加性白高斯噪声(AWGN：AdditiveWhite Gaussian Noise)的干扰，设噪声为w(n)，(n＝0，1，…，N-1)，去掉CP之后，接收到的时域信号r(n)为：The SC-FDE system sends a frame of time-domain signal at the sending end as s(n), (n=0, 1,..., N-1), through the time-varying multipath channel, the impulse response of the channel is h(n) , (n=0, 1,...L-1), the signal transmission process is interfered by additive white Gaussian noise (AWGN: AdditiveWhite Gaussian Noise), let the noise be w(n), (n=0, 1,... , N-1), after removing the CP, the received time-domain signal r(n) is:

$r r ((n no)) = = s the s ((n no)) &CircleTimes; &CircleTimes; h h ((n no)) + + w w ((n no)),, ((n no = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, N N - - 11)) - - - - - - ((11))$

其中，

表示循环卷积运算。in,

Represents a circular convolution operation.

在接收端对信号做离散傅立叶变换(以下简称DFT：Discrete Fourier Transform)变换到频域，根据DFT的时域卷积定理，所得到的频域信号为At the receiving end, the discrete Fourier transform (hereinafter referred to as DFT: Discrete Fourier Transform) is used to transform the signal into the frequency domain. According to the time domain convolution theorem of DFT, the obtained frequency domain signal is

R(k)＝S(k)·H(k)+W(k)，(k＝0，1，…，N-1) (2)R(k)＝S(k)·H(k)+W(k), (k＝0, 1,..., N-1) (2)

其中，R(k)，S(k)，H(k)，W(k)分别是r(n)，s(n)，h(n)，w(n)做N点DFT的频域符号，并且，H(k)，(k＝0，1，…，N-1)是信道的频域响应。经过迫零均衡以后的频域信号为Among them, R(k), S(k), H(k), W(k) are the frequency domain symbols of r(n), s(n), h(n), w(n) for N-point DFT respectively , and, H(k), (k=0, 1, . . . , N-1) is the frequency domain response of the channel. The frequency domain signal after zero-forcing equalization is

$\overset{~ ~}{S S} ((k k)) = = S S ((k k)) + + \frac{W W ((k k))}{H h ((k k))} = = S S ((k k)) + + \overset{~ ~}{W W} ((k k)),, ((k k = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, N N - - 11)) - - - - - - ((33))$

最后，将信号做离散傅里叶逆变换(以下简称IDFT：Inverse Discrete Fourier Transform)变回时域进行判决，得到发送端传输的数据。Finally, the signal is transformed back to the time domain by inverse discrete Fourier transform (hereinafter referred to as IDFT: Inverse Discrete Fourier Transform) for judgment, and the data transmitted by the sender is obtained.

从(3)式可以看出，最终得到的信号与发送的真实信号相比存在误差，这种误差是由噪声引起的，尤其在信道存在深衰点的情况下会过分放大噪声，另外，使用MMSE均衡时会使信号产生畸变。如果在SC-FDE系统中利用了信道状态信息，这些问题就得到缓解。因此，申请人提出了一种选频方式的单载波分块传输方法(已申请国家发明专利，专利申请号：200410036439.6)，克服了传统SC-FDE系统不能利用信道状态信息的缺点，这种新的SC-FDE系统具有更高的系统性能和效率。It can be seen from formula (3) that there is an error between the final signal and the real signal sent. This error is caused by noise, especially when there is a deep fading point in the channel, the noise will be over-amplified. In addition, using MMSE equalization will distort the signal. These problems are alleviated if channel state information is utilized in SC-FDE systems. Therefore, the applicant proposed a frequency-selective single-carrier block transmission method (has applied for a national invention patent, patent application number: 200410036439.6), which overcomes the shortcomings of the traditional SC-FDE system that cannot use channel state information. The SC-FDE system has higher system performance and efficiency.

这种选频方式的单载波分块传输方法的实现步骤分为：The implementation steps of the single-carrier block transmission method in this frequency selection mode are divided into:

第一步，找出可用子信道，并将信道是否可用做标记，然后将子信道标记信息通过反向信道发送给发送端The first step is to find out the available sub-channel and mark whether the channel is available, and then send the sub-channel marking information to the sender through the reverse channel

接收端根据估计出的信道状态信息H(k)，(k＝0，1，…，N-1)，从N个子信道中，按照幅度增益从大到小选出M(M≤N)个可用子信道，设这M个可用子信道的标号为k_i(i＝0，1，…，M-1)，而将剩下的子信道禁用，用1比特信息，即“0”或“1”标记每个子信道是可用还是不可用，这就是发送端所需要的子信道标记信息，如果接收端作N点的DFT，即共有N个子信道，反馈给发送端的子信道标记信息共有N比特，然后将这N比特信息通过反向信道发回发送端。According to the estimated channel state information H(k), (k=0, 1, ..., N-1), the receiving end selects M (M≤N) sub-channels from N sub-channels according to the amplitude gain from large to small Available sub-channels, set the labels of these M available sub-channels as _ki (i=0, 1, ..., M-1), and disable the remaining sub-channels, using 1-bit information, namely "0" or "1" marks whether each sub-channel is available or unavailable. This is the sub-channel marking information required by the sending end. If the receiving end performs N-point DFT, that is, there are N sub-channels in total, and the sub-channel marking information fed back to the sending end has a total of N bits. , and then send the N-bit information back to the sender through the reverse channel.

第二步，根据子信道标记信息改变信号频谱The second step is to change the signal spectrum according to the sub-channel label information

在发送端收到接收端发送回来的子信道标记信息后，就可以用M个可用子信道来传输信号，这样对一帧M个SC-FDE符号s(n)，(n＝0，1，…，M-1)，作M点DFT变换到频域：After the sending end receives the sub-channel label information sent back by the receiving end, it can use M available sub-channels to transmit signals, so for M SC-FDE symbols s(n) in one frame, (n=0, 1, ..., M-1), do M-point DFT transformation to the frequency domain:

$S S ((i i)) = = {Σ Σ}_{n no = = 00}^{M m - - 11} s the s ((n no)) {e e}^{- - j j \frac{22 π π}{M m} ni ni},, ((i i = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, M m - - 11)) - - - - - - ((44))$

就得到M点的频域信号，用选出来的第k_i，(i＝0，1，…，M-1)个可用子信道H(k_i)，(i＝0，1，…，M-1)传输第i个频域信号S(i)，(i＝0，1，…，M-1)，即在可用子信道对应的信号频谱点上放置要传输的频域信号，而将禁用子信道对应的信号频谱点置零，也可以填充一些非信息数据，这样就得到一帧新的频域信号S′(k)，(k＝0，1，…，N-1)，点数为N：The frequency domain signal of M points is obtained, and the selected k _i , (i=0, 1, ..., M-1) available sub-channels H(k _i ), (i = 0, 1, ..., M -1) Transmit the i-th frequency domain signal S(i), (i=0, 1, ..., M-1), that is, place the frequency domain signal to be transmitted on the signal spectrum point corresponding to the available subchannel, and place The signal spectrum points corresponding to the disabled sub-channels are set to zero, and some non-information data can also be filled, so that a new frame of frequency domain signal S'(k), (k=0, 1, ..., N-1), the number of points for N:

${S S}^{' '} ((k k)) = = \{\begin{matrix} S S ((i i)),, & k k = = {k k}_{i i} \\ 00,, & k k &NotEqual; &NotEqual; {k k}_{i i} \end{matrix},, ((k k = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, N N - - 11)) - - - - - - ((55))$

然后，对S′(k)，(k＝0，1，…，N-1)作N点IDFT：Then, do N-point IDFT on S'(k), (k=0, 1, ..., N-1):

${s the s}^{' '} ((n no)) = = \frac{11}{N N} {Σ Σ}_{k k = = 00}^{N N - - 11} {S S}^{' '} ((k k)) {e e}^{j j \frac{22 π π}{N N} nk nk},, ((n no = = 0,1 0,1,, \cdot &Center Dot; \cdot \cdot \cdot &Center Dot;,, N N - - 11)) - - - - - - ((66))$

变成时域信号，过抽样时IDFT点数要大于N，高频部分置零，对该时域信号作D/A后，再进行调制发送出去。It becomes a time-domain signal. When oversampling, the number of IDFT points must be greater than N, and the high-frequency part is set to zero. After D/A is performed on the time-domain signal, it is modulated and sent out.

第三步，选出可用子信道上传输的信号，然后对选出来的信号进行均衡，并变换回时域进行判决，最终得到传输的数据。The third step is to select the signal that can be transmitted on the sub-channel, then equalize the selected signal, and transform it back to the time domain for judgment, and finally obtain the transmitted data.

接收端接收到信号，去掉CP后的时域离散信号为：The receiving end receives the signal, and the time-domain discrete signal after removing the CP is:

${r r}^{' '} ((n no)) = = {s the s}^{' '} ((n no)) &CircleTimes; &CircleTimes; h h ((n no)) + + w w ((n no)),, ((n no = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, N N - - 11)) - - - - - - ((77))$

对其作N点的DFT：Do N-point DFT on it:

${R R}^{' '} ((k k)) = = {Σ Σ}_{n no = = 00}^{N N - - 11} {r r}^{' '} ((n no)) {e e}^{- - j j \frac{22 π π}{N N} nk nk},, ((k k = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, N N - - 11)) - - - - - - ((88))$

并且：and:

R′(k)＝S′(k)H(k)+W(k)，(k＝0，1，…，N-1) (9)R'(k)=S'(k)H(k)+W(k), (k=0, 1,..., N-1) (9)

这样就可以根据子信道标记信息选出M个可用子信道上的信号R′(k_i)，(i＝0，1，…，M-1)，然后用估计出来的信道状态信息中可用子信道参数H(k_i)，(i＝0，1，…，M-1)，对选出来的信号进行均衡；可以选择下述三种均衡方式之一：In this way, the signals R′(k _i ), (i=0, 1, ..., M-1) on M available sub-channels can be selected according to the sub-channel label information, and then the available sub-channels in the estimated channel state information can be used Channel parameters H(k _i ), (i=0, 1, ..., M-1), equalize the selected signal; one of the following three equalization methods can be selected:

1、迫零均衡，1. Zero-forcing equilibrium,

2、最小均方误差均衡，2. Minimum mean square error equalization,

3、混合均衡，即一部分子信道用迫零均衡，而另一部分子信道用最小均方误差均衡；3. Mixed equalization, that is, some sub-channels are equalized by zero-forcing, while the other part of the sub-channels are equalized by minimum mean square error;

以迫零均衡为例作介绍：Take zero-forcing equilibrium as an example for introduction:

${\overset{~ ~}{S S}}^{' '} (({k k}_{i i})) = = \frac{{R R}^{' '} (({k k}_{i i}))}{H h (({k k}_{i i}))},, ((i i = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, M m - - 11)) - - - - - - ((1010))$

令make

$\overset{~ ~}{S S} ((i i)) = = {\overset{~ ~}{S S}}^{' '} (({k k}_{i i})),, ((i i = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, M m - - 11)) - - - - - - ((1111))$

对其作M点的IDFT：IDFT of M points on it:

$\overset{~ ~}{s the s} ((n no)) = = \frac{11}{M m} {Σ Σ}_{i i = = 00}^{M m - - 11} \overset{~ ~}{S S} ((i i)) {e e}^{j j \frac{22 π π}{M m} ni ni},, ((n no = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, M m - - 11)) - - - - - - ((1212))$

对这组数据进行判决就可以恢复出原始数据。The original data can be recovered by making a judgment on this set of data.

(三)发明内容 (3) Contents of the invention

选频方式的单载波分块传输方法利用信道状态信息，对频率选择性衰落信道可以避开深衰点，从而显著改善了系统的性能。通信系统普遍有一定的误码性能要求，而决定系统误码性能的参数是可以获得的均衡后信噪比，即均衡后信号功率和噪声功率的比值。因此本发明提出了一种基于选频方式的单载波分块传输系统的功率控制方法，在保证均衡后信噪比满足系统误码性能要求的情况下，尽可能的减少发送信号功率，可以有效节省发送功率。The frequency-selective single-carrier block transmission method uses channel state information to avoid deep fading points for frequency-selective fading channels, thereby significantly improving system performance. Communication systems generally have certain bit error performance requirements, and the parameter that determines the system bit error performance is the obtained equalized signal-to-noise ratio, that is, the ratio of the equalized signal power to the noise power. Therefore, the present invention proposes a power control method for a single-carrier block transmission system based on a frequency selection method. Under the condition that the signal-to-noise ratio after equalization meets the system error performance requirements, the transmission signal power can be reduced as much as possible, which can effectively Save transmit power.

该功率控制的方法包括以下步骤：The method of power control includes the following steps:

(1)收发双方建立通信后，接收端根据调制方式和要求达到的系统性能即误码率，计算出相应所需的均衡后信噪比，即均衡后信号功率和噪声功率的比值，记为SNR_eq。(1) After the two parties establish communication, the receiving end calculates the corresponding signal-to-noise ratio after equalization according to the modulation method and the required system performance, that is, the bit error rate, that is, the ratio of the signal power after equalization to the noise power, which is recorded as SNR _eq .

(2)接收端根据得到的信道状态信息选取可用子信道，在保证均衡后信噪比为SNR_eq时，计算出所需的接收信噪比，再通过接收信噪比和链路衰耗计算出发端所需的信号功率，称该发端所需的信号功率为功率控制信息P_T，通过反馈信道传送给发送端。(2) The receiving end selects the available sub-channels according to the obtained channel state information, and calculates the required receiving SNR when the SNR after equalization is guaranteed to be SNR _eq , and then calculates through the receiving SNR and link attenuation The signal power required by the originating end is referred to as power control information _PT , which is transmitted to the sending end through a feedback channel.

(3)发送端根据接收到的功率控制信息和子信道标记信息，调节发送功率，发送信号。(3) The sending end adjusts the sending power and sends the signal according to the received power control information and sub-channel label information.

下面对以上步骤作详细说明：The above steps are described in detail below:

第(1)步，接收端根据调制方式和要求达到的系统性能计算所需的均衡后信噪比Step (1), the receiving end calculates the required equalized SNR according to the modulation method and the required system performance

经分析，SC-FDE系统具有很强的抗干扰能力，当信道估计误差和同步误差可以忽略时，接收端均衡后，将多径信道等价为高斯信道，相当于整个系统只受到白高斯噪声的干扰，高斯信道中采用不同调制方式达到要求误码率所需要的信噪比，即为该系统所需的均衡后信噪比SNR_eq，其计算方法在一般的教科书中就可以找到，例如John.G.Proakis所著，由麦格劳-希尔公司(The McGraw-Hill Companies.Inc)出版的《数字通信》(第四版)(DigitalCommunications 4^th Edition)第254-283页；当考虑信道估计误差和同步误差时，可以通过测量估计出实际系统的误差范围和损失的信噪比，损失信噪比的计算方法可以参考有关文献，这时要适当增加SNR_eq以抵消由于这些误差损失的信噪比。After analysis, the SC-FDE system has a strong anti-interference ability. When the channel estimation error and synchronization error can be ignored, after the receiver equalizes, the multipath channel is equivalent to a Gaussian channel, which is equivalent to the whole system being only affected by white Gaussian noise. interference, the Gaussian channel uses different modulation methods to achieve the required signal-to-noise ratio for the required bit error rate, that is, the equalized signal-to-noise ratio SNR _eq required by the system, and its calculation method can be found in general textbooks, such as John. G. Proakis, Digital Communications ^4th Edition, The McGraw-Hill Companies, Inc. pp. 254-283; when considering For channel estimation error and synchronization error, the error range and loss SNR of the actual system can be estimated by measuring. The calculation method of loss SNR can refer to relevant literature. At this time, SNR _eq should be appropriately increased to offset the loss due to these errors signal-to-noise ratio.

第(2)步，接收端根据信道状态信息及所需的均衡后信噪比和链路衰耗计算出发送端所需的信号功率，形成功率控制信息In step (2), the receiving end calculates the signal power required by the sending end according to the channel state information and the required equalized signal-to-noise ratio and link attenuation, and forms power control information

均衡后信噪比决定系统误码率，而均衡后信噪比是由接收信噪比和均衡方式决定的。均衡方式不同，均衡后信号功率和噪声功率就不同，需要的接收信噪比也不同，而接收信噪比和链路衰耗决定发端所需的信号功率，则发端所需的信号功率也就不同；其中，接收信噪比的测量和计算方法可以参照相关文献，下面以迫零均衡为例，说明计算发端所需的信号功率的方法：The SNR after equalization determines the bit error rate of the system, and the SNR after equalization is determined by the received SNR and the equalization method. The equalization method is different, the signal power and noise power after equalization are different, and the required receiving signal-to-noise ratio is also different, and the receiving signal-to-noise ratio and link attenuation determine the signal power required by the transmitting end, and the signal power required by the transmitting end is also Different; among them, the measurement and calculation method of the receiving signal-to-noise ratio can refer to the relevant literature. The following uses zero-forcing equalization as an example to illustrate the method of calculating the signal power required by the transmitter:

假设白高斯噪声双边功率谱密度

(W/Hz)，接收端根据信道估计得到的信道状态信息H(k)，(k＝0，1，…，N-1)，按照幅度增益从大到小选出M(M≤N)个可用子信道，设选取的M个子信道下标为k_i，(i＝0，1，…，M-1)，这些子信道的信道增益为|H(k_i)|，(i＝0，1，…，M-1)。则均衡后每帧的噪声总功率为，以瓦为单位：Assuming white Gaussian noise bilateral power spectral density

(W/Hz), the receiver selects M (M≤N) according to the amplitude gain from large to small according to the channel state information H(k) obtained by channel estimation, (k=0, 1, ..., N-1) available sub-channels, let the selected M sub-channels be subscripted as k _i , (i=0, 1, ..., M-1), and the channel gains of these sub-channels are |H(k _i )|, (i=0 , 1, ..., M-1). The total noise power per frame after equalization is then, in watts:

${σ σ}^{22} = = E E. (({Σ Σ}_{i i = = 00}^{M m - - 11} {| | \frac{N N (({k k}_{i i}))}{H h (({k k}_{i i}))} | |}^{22})) = = \frac{{N N}_{00}}{22} {Σ Σ}_{i i = = 00}^{M m - - 11} {| | \frac{11}{H h (({k k}_{i i}))} | |}^{22} - - - - - - ((1313))$

已知所需的均衡后信噪比为SNR_eq，则每帧所需的接收信号功率为，以瓦为单位：Knowing that the required equalized signal-to-noise ratio is SNR _eq , the required received signal power per frame is, in watts:

${P P}_{R R} = = {σ σ}^{22} \cdot &Center Dot; {SNR SNR}_{eq eq} = = \frac{{N N}_{00}}{22} \cdot &Center Dot; {SNR SNR}_{eq eq} {Σ Σ}_{i i = = 00}^{M m - - 11} {| | \frac{11}{H h (({k k}_{i i}))} | |}^{22} - - - - - - ((1414))$

考虑链路衰耗，设链路衰耗为L，则发端所需的信号功率为，以瓦为单位：Considering the link attenuation, if the link attenuation is L, then the signal power required by the transmitter is, in watts:

${P P}_{T T} = = \frac{{P P}_{R R}}{L L} = = \frac{{N N}_{00}}{22} \cdot &Center Dot; \frac{11}{L L} \cdot &Center Dot; {SNR SNR}_{eq eq} {Σ Σ}_{i i = = 00}^{M m - - 11} {| | \frac{11}{H h (({k k}_{i i}))} | |}^{22} - - - - - - ((1515))$

通过反馈信道将这个功率值形成功率控制信息传给发送端。The power value forms power control information and is transmitted to the sending end through the feedback channel.

第(3)步，发送端根据接收到的功率控制信息和子信道标记信息，调节发送功率，选取可用子信道，发送信号In step (3), the sending end adjusts the sending power according to the received power control information and sub-channel label information, selects available sub-channels, and sends signals

发送端根据接收到的功率控制信息，使发送总功率等于反馈的发端所需的信号功率，发送信号；在实际应用中，系统的发送功率应略大于反馈的发端所需的信号功率，留有一定余量，以保证信噪比控制的比较稳定，达到系统要求。According to the received power control information, the sending end makes the total sending power equal to the signal power required by the sending end of the feedback, and sends the signal; in practical applications, the sending power of the system should be slightly greater than the signal power required by the sending end of the feedback, leaving A certain margin is required to ensure that the signal-to-noise ratio control is relatively stable and meets the system requirements.

本发明基于选频方式的单载波分块传输系统，根据所得到的信道状态信息，通过改变发端所需的信号功率控制接收端均衡后信噪比为一个定值来控制误码率为一个定值，从而实现对发端所需的信号功率的控制。这样，根据信道状态的好坏改变发端所需的信号功率，进一步提高了功率利用率。The single-carrier block transmission system based on the frequency selection mode of the present invention, according to the obtained channel state information, controls the signal-to-noise ratio at the receiving end to be a constant value after equalization by changing the signal power required by the sending end to control the bit error rate to a constant value. value, so as to realize the control of the signal power required by the sending end. In this way, the signal power required by the transmitting end is changed according to the quality of the channel state, and the power utilization rate is further improved.

(四)附图说明 (4) Description of drawings

图1是实现本发明所提出方法的系统框图。Fig. 1 is a block diagram of a system implementing the method proposed by the present invention.

图2是采取16QAM调制方式，选取208个可用子信道，控制误码率为10^-4时的接收信噪比曲线。Fig. 2 is the receiving signal-to-noise ratio curve when the 16QAM modulation mode is adopted, 208 available sub-channels are selected, and the bit error rate is controlled to be 10 ^-4 .

图3是采取16QAM调制方式，选取208个可用子信道，控制误码率为10^-4时仿真所得到的误码率。Fig. 3 adopts 16QAM modulation mode, selects 208 available sub-channels, and controls the bit error rate obtained by simulation when the bit error rate is 10 ^-4 .

图中：1.信源模块，2.符号映射模块，3.FFT模块(M点)，4.信号频谱变换模块，5.IFFT模块(N点)，6.功率控制模块，7.加循环前缀(CP)模块，8.D/A模块，9.中频及射频调制模块，10.信道，11.射频及中频解调模块，12.A/D模块，13.去CP模块，14.增益控制模块，15.FFT模块(N点)，16.信号频谱反变换模块，17.均衡模块，18.IFFT模块(M点)，19.判决模块，20.信道估计及信号功率计算模块，21.同步模块，22.反向信道In the figure: 1. Source module, 2. Symbol mapping module, 3. FFT module (M point), 4. Signal spectrum transformation module, 5. IFFT module (N point), 6. Power control module, 7. Adding cycle Prefix (CP) module, 8. D/A module, 9. IF and RF modulation module, 10. Channel, 11. RF and IF demodulation module, 12. A/D module, 13. Remove CP module, 14. Gain Control module, 15. FFT module (N point), 16. Signal spectrum inverse transformation module, 17. Equalization module, 18. IFFT module (M point), 19. Judgment module, 20. Channel estimation and signal power calculation module, 21 .synchronous module, 22. reverse channel

(五)具体实施方式 (5) Specific implementation methods

图1给出了实现本发明所提出方法的系统框图，各模块作用如下：Fig. 1 has provided the system block diagram realizing the proposed method of the present invention, and each module effect is as follows:

信源模块1：产生要传输的数据。Source module 1: Generates data to be transmitted.

符号映射模块2：调制方式选择QAM或者MPSK时，将信源产生的数据映射到星座图对应点上。Symbol mapping module 2: When the modulation mode is QAM or MPSK, map the data generated by the source to the corresponding point of the constellation diagram.

M点FFT模块3：将每帧M个已映射信号变换到频域，得到信号的M点的频域信号。M-point FFT module 3: Transform the M mapped signals of each frame into the frequency domain to obtain the M-point frequency domain signals of the signal.

信号频谱变换模块4：根据接收端通过反向信道22发送回来的子信道标记信息，将模块3输出的M点频域信号放置到M个可用子信道对应频谱点上，而禁用子信道对应频谱点置零，或填充非信息数据，就得到一帧N点新的SC-FDE频域信号。此模块需要按照背景技术中提到的发明专利(专利申清号：200410036439.6)介绍的方法编程，由通用数字信号处理芯片实现。Signal spectrum conversion module 4: according to the subchannel label information sent back by the receiving end through the reverse channel 22, place the M point frequency domain signal output by module 3 on the spectrum points corresponding to the M available subchannels, and disable the corresponding spectrum of the subchannels If the points are set to zero or filled with non-information data, a new SC-FDE frequency domain signal of N points in a frame is obtained. This module needs to be programmed according to the method introduced in the invention patent (patent application number: 200410036439.6) mentioned in the background technology, and it is realized by a general-purpose digital signal processing chip.

N点IFFT模块5：将新得到的频域信号再变换到时域。N-point IFFT module 5: Transform the newly obtained frequency domain signal into the time domain.

功率控制模块6：根据接收到的功率控制信息调节发送信号功率。Power control module 6: adjust the power of the transmitted signal according to the received power control information.

加CP模块7：将得到的每帧数据加上循环前缀。Add CP module 7: Add a cyclic prefix to each frame of data obtained.

D/A模块8：将数字信号变换为模拟信号。D/A module 8: Convert digital signal to analog signal.

中频及射频调制模块9：如果在无线环境下使用该系统，需要对信号作射频调制才能送天线发射。有的时候需要先把信号调制到中频上进行中频放大，再作射频调制，最后将已调信号送天线发射。如果在有线环境(例如：xDSL)下使用该系统，则不需要作射频调制，也不需要天线发射信号，但也要把信号频谱搬移到语音信道频带以外，保证在传输数据的同时不影响话音传输。IF and RF modulation module 9: If the system is used in a wireless environment, the signal needs to be modulated by RF to send it to the antenna for transmission. Sometimes it is necessary to modulate the signal to the intermediate frequency for intermediate frequency amplification, then perform radio frequency modulation, and finally send the modulated signal to the antenna for transmission. If the system is used in a wired environment (for example: xDSL), there is no need for radio frequency modulation, and there is no need for antennas to transmit signals, but the signal spectrum must also be moved outside the frequency band of the voice channel to ensure that the voice is not affected while transmitting data transmission.

信道10：传输信号的有线信道或无线信道。Channel 10: A wired or wireless channel for transmitting signals.

同步模块21：通过参数估计(例如：盲估计和基于辅助数据的估计)的方法得到系统需要的各种同步数据。同步模块将频率同步数据送给射频及中频解调模块11；将抽样率同步数据送给模数转换模块12；将定时同步数据送给去CP模块13。Synchronization module 21: Obtain various synchronization data required by the system through parameter estimation (for example: blind estimation and estimation based on auxiliary data). The synchronization module sends the frequency synchronization data to the radio frequency and intermediate frequency demodulation module 11 ; sends the sampling rate synchronization data to the analog-to-digital conversion module 12 ; and sends the timing synchronization data to the CP module 13 .

射频及中频解调模块11：在无线环境中，将接收天线接收下来的信号频谱从射频或者中频搬移到低频。在解调之前需要用频率同步数据纠正信号传输过程中引起的频偏。Radio frequency and intermediate frequency demodulation module 11: In a wireless environment, move the signal spectrum received by the receiving antenna from radio frequency or intermediate frequency to low frequency. Before demodulation, it is necessary to use frequency synchronization data to correct the frequency deviation caused in the signal transmission process.

A/D模块12：将解调后模拟信号变换为数字信号。A/D需要对模拟信号进行抽样，提供时钟信号的晶振需要跟发射机D/A模块的晶振频率相同，否则就会导致抽样率误差。因此在A/D之前要进行抽样率同步。A/D module 12: convert the demodulated analog signal into a digital signal. The A/D needs to sample the analog signal, and the crystal oscillator that provides the clock signal needs to have the same frequency as the crystal oscillator of the D/A module of the transmitter, otherwise it will cause a sampling rate error. Therefore, the sampling rate must be synchronized before the A/D.

去CP模块13：将循环前缀去掉。这时就存在判断一帧数据何时开始的问题，因此去CP之前需要作定时同步。Go to CP module 13: remove the cyclic prefix. At this time, there is a problem of judging when a frame of data starts, so timing synchronization is required before going to the CP.

增益控制模块14：根据功率控制信息，消除功率控制对信号星座点的影响。Gain control module 14: Eliminate the influence of power control on signal constellation points according to the power control information.

N点FFT模块15：将去掉CP的信号变换到频域。N-point FFT module 15: Transform the CP-removed signal into the frequency domain.

信道估计及发送信号功率计算模块20：跟同步类似，也需要通过参数估计来得到CSI，常用的一般是盲信道估计和基于辅助数据的信道估计。估计出CSI后选出可用子信道，将这些可用子信道参数送给均衡模块17；同时根据信道是否可用，用1比特信息(“0”或“1”)标记，形成子信道标记信息，将子信道标记信息同时送给信号频谱反变换模块16和反向信道22，通过反向信道发回发送端的信号频谱变换模块4；根据达到不同误码率所需的均衡后信噪比计算出所需的发送信号功率，传给增益控制模块14和反向信道22，通过反向信道发回发送端的功率控制模块6。此模块的功率控制部分需要按照本发明介绍的方法编程，由通用数字信号处理芯片实现。Channel estimation and transmission signal power calculation module 20: Similar to synchronization, it is also necessary to obtain CSI through parameter estimation. Commonly used are blind channel estimation and channel estimation based on auxiliary data. After estimating the CSI, the available sub-channels are selected, and these available sub-channel parameters are sent to the equalization module 17; at the same time, according to whether the channel is available, it is marked with 1-bit information ("0" or "1") to form sub-channel marking information, and the The sub-channel label information is sent to the signal spectrum inverse conversion module 16 and the reverse channel 22 at the same time, and is sent back to the signal spectrum conversion module 4 at the sending end through the reverse channel; The required transmission signal power is transmitted to the gain control module 14 and the reverse channel 22, and sent back to the power control module 6 at the transmitting end through the reverse channel. The power control part of this module needs to be programmed according to the method introduced in the present invention, and is realized by a general digital signal processing chip.

信号频谱反变换模块16：根据信道估计及发送信号功率计算模块20送来的子信道标记信息，找出接收信号中由可用子信道携带的M点频域信号。此模块需要按照背景技术中提到的发明专利(专利申请号：200410036439.6)介绍的方法编程，由通用数字信号处理芯片实现。Signal spectrum inverse transformation module 16: According to the subchannel label information sent by the channel estimation and transmission signal power calculation module 20, find out the frequency domain signals of M points carried by available subchannels in the received signal. This module needs to be programmed according to the method introduced in the invention patent (patent application number: 200410036439.6) mentioned in the background technology, and it is realized by a general digital signal processing chip.

均衡模块17：用信道估计及发送信号功率计算模块20送来的可用子信道参数，对信号频谱反变换模块16选出来的信号进行均衡。均衡方式可以选择下述三种均衡方式之一：迫零均衡、最小均方误差均衡、混合均衡(即：一部分子信道用迫零均衡，而另一部分子信道用最小均方误差均衡)。Equalization module 17: using the available sub-channel parameters sent by the channel estimation and transmission signal power calculation module 20, to equalize the signal selected by the signal spectrum inverse transformation module 16. The equalization method can choose one of the following three equalization methods: zero-forcing equalization, minimum mean square error equalization, and mixed equalization (that is, some sub-channels use zero-forcing equalization, while other sub-channels use minimum mean square error equalization).

M点IFFT模块18：将均衡后信号的M个频域信号变换到时域。M-point IFFT module 18: Transform M frequency domain signals of the equalized signal into time domain.

判决模块19：根据星座图完成时域信号的判决。Judgment module 19: complete the judgment of the time domain signal according to the constellation diagram.

反向信道22：将子信道标记信息和功率控制信息发回发送端。Reverse channel 22: Send subchannel label information and power control information back to the sender.

当信道估计误差和同步误差可以忽略时，接收端均衡后，将多径信道等价为高斯信道，相当于整个系统只受到白高斯噪声的干扰，高斯信道中采用不同调制方式达到要求误码率所需要的信噪比，即为该系统所需的均衡后信噪比SNR_eq；高斯信道中的误码率计算可以参照John.G.Proakis所著，由麦格劳-希尔公司(The McGraw-Hill Companies.Inc)出版的《数字通信》(第四版)(Digital Communications 4^th Edition)第278页。When the channel estimation error and synchronization error can be ignored, after equalization at the receiving end, the multipath channel is equivalent to a Gaussian channel, which means that the entire system is only interfered by white Gaussian noise, and different modulation methods are used in the Gaussian channel to achieve the required bit error rate. The required signal-to-noise ratio is the required equalized signal-to-noise ratio SNR _eq of the system; the bit error rate calculation in the Gaussian channel can be written with reference to John.G.Proakis, by McGraw-Hill Company (The 278, Digital Communications ^4th Edition, McGraw-Hill Companies, Inc.

该实施例仿真参数：The simulation parameters of this embodiment:

仿真环境：Matlab7.0Simulation environment: Matlab7.0

子信道总数：N＝256Total number of sub-channels: N=256

可用子信道数，即每帧SC-FDE数据符号数：M＝208。The number of available sub-channels, that is, the number of SC-FDE data symbols per frame: M=208.

CP长度：32CP length: 32

符号映射：16QAMSymbol mapping: 16QAM

控制的误码率为：10^-4 Controlled bit error rate: 10 ^-4

链路衰耗：L＝1(即0dB，这里没有考虑链路衰耗)Link attenuation: L=1 (that is, 0dB, link attenuation is not considered here)

同步和信道估计：理想估计，即同步参数和信道估计结果不存在误差Synchronization and channel estimation: ideal estimation, that is, there is no error in the synchronization parameters and channel estimation results

在不考虑链路衰耗和同步参数以及信道估计误差的情况下，能更清楚地说明本发明的技术效果。The technical effects of the present invention can be explained more clearly without considering link attenuation, synchronization parameters and channel estimation errors.

图2和图3给出了本发明的该实施例在100个信道样本中的接收信噪比曲线和所控制的误码率情况，其中信道样本取自SUI-5信道(IEEE 802.16标准中建议的测试信道之一)，其中图2信噪比SNR的单位是dB。从仿真结果中可以看出，在经过这100个不同信道样本时，接收信噪比的最大值和平均值之间相差大约3.1dB(图2中纵坐标18.65dB附近的水平横线表示平均接收信噪比)。如果不采取功率控制方法，系统往往按照最坏的信道状况设计发送信号功率以保证有稳定的误码性能。这说明如果系统采用了功率控制方法可以比不采用该方法大幅度的节省功率，本发明的功率控制方法在本实施例中的仿真条件下可以节约大约3.1dB的发射功率。并且从图3中可以看出该实施例可以将误码率控制的相对比较稳定。Fig. 2 and Fig. 3 have provided this embodiment of the present invention in the received SNR curve and the bit error rate situation of control in 100 channel samples, and wherein channel sample is taken from SUI-5 channel (recommended in IEEE 802.16 standard One of the test channels), where the unit of the signal-to-noise ratio SNR in Figure 2 is dB. It can be seen from the simulation results that the difference between the maximum value and the average value of the received signal-to-noise ratio is about 3.1dB when passing through these 100 different channel samples (the horizontal line near the ordinate 18.65dB in Figure 2 represents the average received signal-to-noise ratio). If no power control method is adopted, the system usually designs the transmission signal power according to the worst channel condition to ensure stable bit error performance. This shows that if the system adopts the power control method, the power can be greatly saved compared with that without this method. The power control method of the present invention can save about 3.1 dB of transmit power under the simulation conditions in this embodiment. And it can be seen from FIG. 3 that this embodiment can control the bit error rate relatively stably.

为避免混淆，本说明书中所提到的一些名词做以下解释：To avoid confusion, some terms mentioned in this manual are explained as follows:

1.均衡后信噪比：均衡之后信号功率跟噪声功率的比值。1. SNR after equalization: The ratio of signal power to noise power after equalization.

2.符号：是指信息比特经过调制映射(也称符号映射)后的数据。一般是一个实部和虚部均为整数的复数。2. Symbol: refers to the data after information bits are modulated and mapped (also called symbol mapping). Usually a complex number whose real and imaginary parts are integers.

3.一帧信号：对于OFDM，一帧信号在发送端是指作IFFT变换的N个符号，在接收端是指在去掉CP以后作FFT变换的N个符号。对于SC-FDE，一帧信号在发送端是指相邻两个CP之间的N个信息符号，在接收端是指在去掉CP以后作FFT变换的N个符号。对于按本发明提出的方法实现的SC-FDE系统，一帧信号在发送端是指作FFT变换的M个符号，在接收端是指在均衡以后作IFFT变换的M个符号。3. One frame signal: For OFDM, one frame signal refers to N symbols that undergo IFFT transformation at the sending end, and at the receiving end refers to N symbols that undergo FFT transformation after removing the CP. For SC-FDE, a frame signal refers to the N information symbols between two adjacent CPs at the sending end, and refers to the N symbols transformed by FFT after removing the CP at the receiving end. For the SC-FDE system realized by the method proposed by the present invention, a frame signal refers to M symbols that are transformed by FFT at the sending end, and refers to M symbols that are transformed by IFFT after equalization at the receiving end.

4.子信道：对于OFDM，SC-FDE基带信号，一个子信道是指在接收端FFT后一个频率点。对于射频信道，一个子信道是指射频信道的一段频谱。4. Sub-channel: For OFDM and SC-FDE baseband signals, a sub-channel refers to a frequency point after FFT at the receiving end. For a radio frequency channel, a subchannel refers to a section of frequency spectrum of the radio frequency channel.

Claims

1. A power control method in a frequency-selective single-carrier block transmission system, characterized in that: the power control method comprises the following steps:

(1) After the two parties establish communication, the receiving end calculates the corresponding signal-to-noise ratio after equalization according to the modulation method and the required system performance, that is, the bit error rate, that is, the ratio of the signal power after equalization to the noise power, which is recorded as SNR _eq ;

(2) The receiving end selects the available sub-channels according to the obtained channel state information, and calculates the required receiving SNR when the SNR after equalization is guaranteed to be SNR _eq , and then calculates through the receiving SNR and link attenuation The signal power required by the originating end is referred to as the power control information _PT , which is transmitted to the sending end through the feedback channel;

(3) The sending end adjusts the sending power and sends the signal according to the received power control information and sub-channel label information.

2. the power control method in the frequency-selective single-carrier block transmission system according to claim 1, is characterized in that: described step (2) adopts following method to realize: after the equalization signal-to-noise ratio determines system bit error rate, and The signal-to-noise ratio after equalization is determined by the receiving signal-to-noise ratio and the equalization method. The equalization method is different, the signal power and noise power are different after equalization, and the required receiving signal-to-noise ratio is also different, while the receiving signal-to-noise ratio and link attenuation Determine the signal power required by the sender, and the signal power required by the sender will be different; the method of calculating the signal power required by the sender is:

Assuming white Gaussian noise bilateral power spectral density

The receiving end selects M according to the channel state information H(k) obtained by channel estimation, k=0, 1, ..., N-1, from large to small according to the amplitude gain, and M≤N available sub-channels, assuming that the selected M Sub-channels are subscripted as k _i , i=0, 1, ..., M-1, and the channel gains of these sub-channels are |H(k _i )|, i = 0, 1, ..., M-1, then after equalization The total noise power per frame is, in watts:

{σ σ}^{22} = = E E. (({Σ Σ}_{i i = = 00}^{M m} {| | \frac{N N (({k k}_{i i}))}{H h (({k k}_{i i}))} | |}^{22})) = = \frac{{N N}_{00}}{22} {Σ Σ}_{i i = = 00}^{M m - - 11} {| | \frac{11}{H h (({k k}_{i i}))} | |}^{22}

Knowing that the required equalized signal-to-noise ratio is SNR _eq , the required received signal power per frame is, in watts:

{P P}_{R R} = = {σ σ}^{22} \cdot \cdot {SNR SNR}_{eq eq} = = \frac{{N N}_{00}}{22} \cdot \cdot {SNR SNR}_{eq eq} {Σ Σ}_{i i = = 00}^{M m - - 11} {| | \frac{11}{H h (({k k}_{i i}))} | |}^{22}

Considering the link attenuation, if the link attenuation is L, then the signal power required by the transmitter is, in watts:

{P P}_{T T} = = \frac{{P P}_{R R}}{L L} = = \frac{{N N}_{00}}{22} \cdot \cdot \frac{11}{L L} \cdot &Center Dot; {SNR SNR}_{eq eq} {Σ Σ}_{i i = = 00}^{M m - - 11} {| | \frac{11}{H h (({k k}_{i i}))} | |}^{22}

The power value forms power control information and is transmitted to the sending end through the feedback channel.

3. The power control method in the frequency-selective single-carrier block transmission system according to claim 1, characterized in that: in the step (3), the sending end makes the total sending power equal to the feedback according to the received power control information The signal power required by the sender to send the signal.