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目录
未来移动通信的滤波器组多载波调制方案
摘要：未来的无线系统将具有广泛的可能用例。这需要对可用的时频资源进行灵活分配，而传统的正交频分复用（OFDM）很难实现这一点。因此，需要对OFDM进行修改，例如窗口化或滤波。另一种选择是采用不同的调制方案，如滤波器组多载波（FBMC）。在本文中，我们提供了一个统一的框架，讨论和评估了FBMC，并将其与基于OFDM的方案进行了比较。我们的研究不仅基于模拟，还通过真实世界的测试平台测量和试验进行了实证，我们展示了FBMC所面临的主要挑战之一——多天线和信道估计可以被有效处理。此外，我们推导了双选择信道中的信号干扰比的闭式解，并表明在许多实际情况下，单点均衡器是足够的。
关键词：FBMC，OQAM，OFDM，波形，MIMO，信道估计，时频分析，测量
未来的移动系统将具有高度异质性，并具有广泛的可能用例，从增强型移动宽带（eMBB）到增强型机器类型通信（eMTC）再到车载通信中的超可靠低延迟通信（URLLC）[1]–[5]。为了有效支持这些多样化的用例，我们需要对可用的时频资源进行灵活分配，如图1所示。在科学界和标准化组织内部都有关于下一代移动通信系统应该使用哪种调制格式的热烈讨论[6]–[9]。最终，3GPP决定他们将在第五代（5G）移动通信中继续使用正交频分复用（OFDM）（做了一些小的修改）[10]，[11]。虽然从OFDM切换到其他方案不会带来数量级的性能提升，但仍然重要进行研究，因为调制格式是每个通信系统的核心，决定了支持的用例。
在本文中，我们将OFDM与滤波器组多载波（FBMC）进行比较[12]–[14]，后者具有更好的频谱特性。FBMC存在不同的变体，但我们将主要关注偏移正交振幅调制（OQAM）[15]，因为它提供了最高的频谱效率。OQAM有不同的名称，如交错多音和余弦调制多音[13]，但本质上都是一样的[16]。详细文章见第4部分。
部分代码：
% Sampling rate: should approximately match the power delay profile of the
% channel and must be larger than "SubcarrierSpacing*NumberOfSubcarriers".
SamplingRate = 15e3*14*14;
dt = 1/SamplingRate;
% Simulation parameters
Simulation_SNR_OFDM_dB = [-5:2.5:30]; % SNR for OFDM in dB. The average transmit power of all methods is the same! However, the SNR might be different due to filtering (in FOFDM and UFMC) or because a different bandwidth is used (different subcarrier spacing or different number of subcarriers).
Simulation_MonteCarloRepetitions = 1000; % Number of Monte Carlo repetitions over which we take the average
% Channel parameters
Channel_Velocity_kmh = 130; % Velocity in km/h. Note that [mph]*1.6=[kmh] and [m/s]*3.6=[kmh]
Channel_PowerDelayProfile = 'VehicularA'; % Power delay profile, either string or vector: 'Flat', 'AWGN', 'PedestrianA', 'PedestrianB', 'VehicularA', 'VehicularB', 'ExtendedPedestrianA', 'ExtendedPedestrianB', or 'TDL-A_xxns','TDL-B_xxns','TDL-C_xxns' (with xx the RMS delay spread in ns, e.g. 'TDL-A_30ns'), or [1 0 0.2] (Self-defined power delay profile which depends on the sampling rate)
Channel_DopplerModel = 'Jakes'; % Which Doppler model: 'Jakes', 'Uniform', 'Discrete-Jakes', 'Discrete-Uniform'. For "Discrete-", we assume a discrete Doppler spectrum to improve the simulation time. This however only works accuratly if the number of samples and the velocity is sufficiently high.
Channel_CarrierFrequency = 2.5e9; % Carrier Frequency (Hz)
% General modulation paramters
QAM_ModulationOrder = 64; % QAM sigal constellation order: 4, 16, 64, 256, 1024,...
% FBMC parameters
FBMC_NumberOfSubcarriers = 24; % Number of subcarriers
FBMC_NumberOfSymbolsInTime = 30; % Number FBMC symbols in time
FBMC_SubcarrierSpacing = 15e3; % Subcarrier spacing (Hz)
FBMC_PrototypeFilter = 'Hermite-OQAM'; % Prototype filter (Hermite, PHYDYAS, RRC) and OQAM or QAM.
FBMC_OverlappingFactor = 4; % Overlapping factor, 2,3,4,...
% OFDM parameters
OFDM_NumberOfSubcarriers = 24; % Number of subcarriers
OFDM_NumberOfSymbolsInTime = 14; % Number OFDM symbols in time
OFDM_SubcarrierSpacing = 15e3; % Subcarrier spacing (Hz)
OFDM_CyclicPrefixLength = 1/(14*OFDM_SubcarrierSpacing); % Length of the cyclic prefix (s)
% WOLA parameters
WOLA_NumberOfSubcarriers = 24; % Number of subcarriers
WOLA_NumberOfSymbolsInTime = 14; % Number WOLA symbols in time
WOLA_SubcarrierSpacing = 15e3; % Subcarrier spacing (Hz)
WOLA_CyclicPrefixLength = 0; % Length of the cyclic prefix (s) to combat the channel
WOLA_WindowLengthTX = 1/(14*2*WOLA_SubcarrierSpacing); % Length of the window overlapping (s) at the transmitter
WOLA_WindowLengthRX = 1/(14*2*WOLA_SubcarrierSpacing); % Length of the window overlapping (s) at the receiver
% FOFDM parameters
FOFDM_NumberOfSubcarriers = 24; % Number of subcarriers
FOFDM_NumberOfSymbolsInTime = 14; % Number FOFDM symbols in time
FOFDM_SubcarrierSpacing = 15e3; % Subcarrier spacing (Hz)
FOFDM_CyclicPrefixLength = 0; % Length of the cyclic prefix (s) to combat the channel
FOFDM_FilterLengthTX = 0.2*1/(FOFDM_SubcarrierSpacing); % Length of the transmit filter (s)
FOFDM_FilterLengthRX = 0.2*1/(FOFDM_SubcarrierSpacing); % Length of the receive filter (s)
FOFDM_FilterCylicPrefixLength = 1/(14*FOFDM_SubcarrierSpacing); % Length of the additional cyclic prefix (s) to combat ISI and ICI due to the filtering
% UFMC parameters
UFMC_NumberOfSubcarriers = 24; % Number of subcarriers
UFMC_NumberOfSymbolsInTime = 14; % Number UFMC symbols in time
UFMC_SubcarrierSpacing = 15e3; % Subcarrier spacing (Hz)
UFMC_CyclicPrefixLength = 0; % Length of the cyclic prefix (s) to combat the channel. If zero padding is used, this length reprents the zero guard length instead of the CP length.
UFMC_FilterLengthTX = 1/14*1/(UFMC_SubcarrierSpacing); % Length of the transmit filter (s)
UFMC_FilterLengthRX = 1/14*1/(UFMC_SubcarrierSpacing); % Length of the receive filter (s)
UFMC_FilterCylicPrefixLength = 1/(14*UFMC_SubcarrierSpacing); % Length of the additional cyclic prefix (or zero guard symbol if ZP is used) in seconds (s). Needed to combat ISI and ICI due to the filtering. However, small ICI and ISI is perfectly feasibly.
UFMC_ZeroPaddingInsteadOfCP = true; % TRUE for Zero Padding (ZP) and FALSE for a conventional Cyclic Prefix (CP). Note that a CP delivers nicer plots of the power spectral density because there are no zero crossing.
%% Generate " +Modulation\" Objects
% FBMC Object
FBMC = Modulation.FBMC(...
FBMC_NumberOfSubcarriers,... % Number of subcarriers
FBMC_NumberOfSymbolsInTime,... % Number FBMC symbols in time
FBMC_SubcarrierSpacing,... % Subcarrier spacing (Hz)
SamplingRate,... % Sampling rate (Samples/s)
0,... % Intermediate frequency of the first subcarrier (Hz). Must be a multiple of the subcarrier spacing
false,... % Transmit real valued signal (sampling theorem must be fulfilled!)
FBMC_PrototypeFilter,... % Prototype filter (Hermite, PHYDYAS, RRC) and OQAM or QAM. The data rate of QAM is reduced by a factor of two compared to OQAM, but robustness in doubly-selective channels is inceased
FBMC_OverlappingFactor, ... % Overlapping factor (also determines oversampling in the frequency domain)
0, ... % Initial phase shift
true ... % Polyphase implementation
);
FBMC_BlockOverlapTime = (FBMC.PrototypeFilter.OverlappingFactor-1/2)*FBMC.PHY.TimeSpacing;
% OFDM Object
OFDM = Modulation.OFDM(...
OFDM_NumberOfSubcarriers,... % Number of subcarriers
OFDM_NumberOfSymbolsInTime,... % Number OFDM symbols in time
OFDM_SubcarrierSpacing,... % Subcarrier spacing (Hz)
SamplingRate,... % Sampling rate (Samples/s)
0,... % Intermediate frequency of the first subcarrier (Hz). Must be a multiple of the subcarrier spacing
false,... % Transmit real valued signal (sampling theorem must be fulfilled!)
OFDM_CyclicPrefixLength, ... % Length of the cyclic prefix (s)
FBMC_BlockOverlapTime ... % Length of the guard time (s), that is, zeros at the beginning and at the end of the transmission
);
% Windowed OFDM (WOLA)
WOLA = Modulation.WOLA(...
WOLA_NumberOfSubcarriers,... % Number subcarriers
WOLA_NumberOfSymbolsInTime,... % Number WOLA symbols in time
WOLA_SubcarrierSpacing,... % Subcarrier spacing (Hz)
SamplingRate,... % Sampling rate (Samples/s)
0,... % Intermediate frequency of the first subcarrier (Hz). Must be a multiple of the subcarrier spacing
false,... % Transmit real valued signal (sampling theorem must be fulfilled!)
0, ... % Length of the cyclic prefix (s)
FBMC_BlockOverlapTime-WOLA_WindowLengthTX/2, ... % Length of the guard time (s), that is, zeros at the beginning and at the end of the transmission
WOLA_WindowLengthTX, ... % Length of the window overlapping (s) at the transmitter
WOLA_WindowLengthRX ... % Length of the window overlapping (s) at the receiver
);
% FOFDM (Filtered OFDM)
FOFDM = Modulation.FOFDM(...
FOFDM_NumberOfSubcarriers,... % Number of subcarriers
FOFDM_NumberOfSymbolsInTime,... % Number FOFDM symbols in time
FOFDM_SubcarrierSpacing,... % Subcarrier spacing (Hz)
SamplingRate,... % Sampling rate (Samples/s)
0,... % Intermediate frequency of the first subcarrier (Hz). Must be a multiple of the subcarrier spacing
false,... % Transmit real valued signal (sampling theorem must be fulfilled!)
0, ... % Length of the cyclic prefix (s)
FBMC_BlockOverlapTime-FOFDM_FilterLengthTX/2, ... % Length of the guard time (s), that is, zeros at the beginning and at the end of the transmission
FOFDM_FilterLengthTX, ... % Length of the transmit filter (s)
FOFDM_FilterLengthRX, ... % Length of the receive filter (s)
FOFDM_FilterCylicPrefixLength ... % Length of the additional cyclic prefix (s). Needed to combat ISI and ICI due to the filtering. However, some small ICI and ISI is perfectly fine.
);
% UFMC (Subband Filtered OFDM)
UFMC = Modulation.UFMC(...
UFMC_NumberOfSubcarriers,... % Number of subcarriers
UFMC_NumberOfSymbolsInTime,... % Number UFMC symbols in time
UFMC_SubcarrierSpacing,... % Subcarrier spacing (Hz)
SamplingRate,... % Sampling rate (Samples/s)
0,... % Intermediate frequency of the first subcarrier (Hz). Must be a multiple of the subcarrier spacing
false,... % Transmit real valued signal (sampling theorem must be fulfilled!)
0, ... % Length of the cyclic prefix (s). If zero padding is used, this length reprents the zero guard length instead of the CP length
FBMC_BlockOverlapTime-UFMC_FilterLengthTX/2, ... % Length of the guard time (s), that is, zeros at the beginning and at the end of the transmission
UFMC_FilterLengthTX, ... % Length of the transmit filter (s)
UFMC_FilterLengthRX, ... % Length of the receive filter (s)
UFMC_FilterCylicPrefixLength, ... % Length of the additional cyclic prefix (or zero guard symbol if ZP is used) in seconds (s). Needed to combat ISI and ICI due to the filtering. However, some small ICI and ISI is perfectly fine.
UFMC_ZeroPaddingInsteadOfCP ... % TRUE for Zero Padding (ZP) or FALSE for a conventional Cyclic Prefix (CP)
);
% Number of samples
N_FBMC = FBMC.Nr.SamplesTotal;
N_OFDM = OFDM.Nr.SamplesTotal;
N_WOLA = WOLA.Nr.SamplesTotal;
N_FOFDM = FOFDM.Nr.SamplesTotal;
N_UFMC = UFMC.Nr.SamplesTotal;
N = max([N_FBMC N_OFDM N_WOLA N_FOFDM N_UFMC]);
ChannelModel = Channel.FastFading(...
SamplingRate,... % Sampling rate (Samples/s)
Channel_PowerDelayProfile,... % Power delay profile, either string or vector: 'Flat', 'AWGN', 'PedestrianA', 'PedestrianB', 'VehicularA', 'VehicularB', 'ExtendedPedestrianA', 'ExtendedPedestrianB', or 'TDL-A_xxns','TDL-B_xxns','TDL-C_xxns' (with xx the RMS delay spread in ns, e.g. 'TDL-A_30ns'), or [1 0 0.2] (Self-defined power delay profile which depends on the sampling rate)
N,... % Number of total samples
Channel_Velocity_kmh/3.6*Channel_CarrierFrequency/2.998e8,... % Maximum Doppler shift: Velocity_kmh/3.6*CarrierFrequency/2.998e8
Channel_DopplerModel,... % Which Doppler model: 'Jakes', 'Uniform', 'Discrete-Jakes', 'Discrete-Uniform'. For "Discrete-", we assume a discrete Doppler spectrum to improve the simulation time. This only works accuratly if the number of samples and the velocity is sufficiently large
100, ... % Number of paths for the WSSUS process. Only relevant for a 'Jakes' and 'Uniform' Doppler spectrum
1,... % Number of transmit antennas
1,... % Number of receive antennas
true ... % Gives a warning if the predefined delay taps of the channel do not fit the sampling rate. This is usually not much of a problem if they are approximatly the same.
);
文章中一些内容引自网络，会注明出处或引用为参考文献，难免有未尽之处，如有不妥，请随时联系删除。
[1]Ronald Nissel (2018) Filter Bank Multicarrier Modulation (FBMC)
